Galvanic series relationships are useful as a guide for selecting metals to be joined, will help the selection of metals having minimal tendency to interact galvanically, or will indicate the need or degree of protection to be applied to lessen the expected potential interactions. In general, the further apart the materials are in the galvanic series, the higher the risk of galvanic corrosion, which should be prevented by design. Conversely, the farther one metal is from another, the greater the corrosion will be. However, the series does not provide any information on the rate of galvanic corrosion and thus serves as a basic qualitative guide only.

  The use of the galvanic series has to be done with
caution and a basic knowledge of the environments
that is a necessary part of this serious form of corrosion. The following documents provide different points of view regarding the ranking of metals and coatings in practical schemes for preventing
galvanic corrosion.

Galvanic Table

The following galvanic table lists metals in the order of their relative activity in seawater environment. The list begins with the more active (anodic) metal and proceeds down the to the least active (cathodic) metal of the galvanic series. A "galvanic series" applies to a particular electrolyte solution, hence for each specific solution which is expected to be encountered for actual use, a different order or series will ensue. In a galvanic couple, the metal higher in the series (or the smaller) represents the anode, and will corrode preferentially in the environment. Listed below is the latest galvanic table from MIL-STD-889 where the materials have been numbered for discussion of characteristics. However, for any combination of dissimilar metals, the metal with the lower number will act as an anode and will corrode preferentially.

Active (Anodic)

1. Magnesium
2. Mg alloy AZ-31B
3. Mg alloy HK-31A
4. Zinc (hot-dip, die cast, or plated)
5. Beryllium (hot pressed)
6. Al 7072 clad on 7075
7. Al 2014-T3
8. Al 1160-H14
9. Al 7079-T6
10. Cadmium (plated)
11. Uranium
12. Al 218 (die cast)
13. Al 5052-0
14. Al 5052-H12
15. Al 5456-0, H353
16. Al 5052-H32
17. Al 1100-0
18. Al 3003-H25
19. Al 6061-T6
20. Al A360 (die cast)
21. Al 7075-T6
22. Al 6061-0
23. Indium
24. Al 2014-0
25. Al 2024-T4
26. Al 5052-H16
27. Tin (plated)
28. Stainless steel 430 (active)
29. Lead
30. Steel 1010
31. Iron (cast)
32. Stainless steel 410 (active)
33. Copper (plated, cast, or wrought)
34. Nickel (plated)
35. Chromium (Plated)
36. Tantalum
37. AM350 (active)
38. Stainless steel 310 (active)
39. Stainless steel 301 (active)
40. Stainless steel 304 (active)
41. Stainless steel 430 (active)
42. Stainless steel 410 (active)
43. Stainless steel 17-7PH (active)
44. Tungsten
45. Niobium (columbium) 1% Zr
46. Brass, Yellow, 268
47. Uranium 8% Mo
48. Brass, Naval, 464
49. Yellow Brass
50. Muntz Metal 280
51. Brass (plated)
52. Nickel-silver (18% Ni)
53. Stainless steel 316L (active)
54. Bronze 220
55. Copper 110
56. Red Brass
57. Stainless steel 347 (active)
58. Molybdenum, Commercial pure
59. Copper-nickel 715
60. Admiralty brass
61. Stainless steel 202 (active)
62. Bronze, Phosphor 534 (B-1)
63. Monel 400
64. Stainless steel 201 (active)
65. Carpenter 20 (active)
66. Stainless steel 321 (active)
67. Stainless steel 316 (active)
68. Stainless steel 309 (active)
69. Stainless steel 17-7PH (passive)
70. Silicone Bronze 655
71. Stainless steel 304 (passive)
72. Stainless steel 301 (passive)
73. Stainless steel 321 (passive)
74. Stainless steel 201 (passive)
75. Stainless steel 286 (passive)
76. Stainless steel 316L (passive)
77. AM355 (active)
78. Stainless steel 202 (passive)
79. Carpenter 20 (passive)
80. AM355 (passive)
81. A286 (passive)
82. Titanium 5A1, 2.5 Sn
83. Titanium 13V, 11Cr, 3Al (annealed)
84. Titanium 6Al, 4V (solution treated and aged)
85. Titanium 6Al, 4V (anneal)
86. Titanium 8Mn
87. Titanium 13V, 11Cr 3Al (solution heat treated and aged)
88. Titanium 75A
89. AM350 (passive)
90. Silver
91. Gold
92. Graphite

End - Noble (Less Active, Cathodic) 

Galvanic Compatibility

Often when design requires that dissimilar metals come in contact, the galvanic compatibility is managed by finishes and plating. The finishing and plating selected facilitate the dissimilar materials being in contact and protect the base materials from corrosion.

• For harsh environments, such as outdoors, high humidity, and salt environments fall into this category. Typically there should be not more than 0.15 V difference in the "Anodic Index". For example; gold - silver would have a difference of 0.15V being acceptable.
• For normal environments, such as storage in warehouses or non-temperature and humidity controlled environments. Typically there should not be more than 0.25 V difference in the "Anodic Index".
• For controlled environments, such that are temperature and humidity controlled, 0.50 V can be tolerated. Caution should be maintained when deciding for this application as humidity and temperature do vary from regions.

Anodic Index

Galvanic Series in Seawater

A galvanic series has been drawn up for metals and alloys in seawater, which shows their relative nobility. The series is based on corrosion potential measurements in seawater. The relative position of the materials can change in other environments. The further apart the materials are in this series, the higher the risk of galvanic corrosion. 

Most cathodic, noble, or resistant to corrosion

• Platinum
• Gold
• Graphite
• Titanium
• Silver
• Chlorimet 3
• Hastelloy C

1. 18-8 Mo stainless steel (passive)
2. 18-8 stainless steel (passive)
3. Chromium steel >11 % Cr (passive)
4. Inconel (passive)
5. Nickel (passive)
6. Silver solder
7. Monel
8. Bronzes
9. Copper
10. Brasses

• Chlorimet 2
• Hastelloy B
• Inconel (active)
• Nickel (active)
• Tin
• Lead
• Lead-tin solders
• 18-8 Mo stainless steel (active)
• 8-8 stainless steel (active)
• Ni-resist
• Chromium steel >11 % Cr (active)

 

1. Cast iron
2. Steel or iron
3. 024 aluminum
4. Cadmium
5. Commercially pure aluminium
6. Zinc
7. Magnesium and its alloys

Most anodic or easy to corrode

Bill Allan of N.A.P.I.T. looks, in this very useful and informative article, at designing electrical installations so that they meet the requirements of the 17th Edition:

Fig 1.Consumer unit - 2x30mA RCDs + 30mA RCBO.

Fig 2. As Fig 1, but fire alarm MCB protected.

Fig 3. As Fig 2 but alarm sysem not shown (not mains op.)

Definitions:

Before we get into specifics, we'd better clarify a few definitions which are important in the design of electrical installations, including those in domestic premises. Part 2 of the Wiring Regulations contains definitions and the following, although they were all in the previous edition of BS 7671, are of particular importance in the 17th Edition and we'll be referring to them in this article:

Skilled person - 'A person with technical knowledge or sufficient experience to enable him/her to avoid dangers which electricity may create'.

Instructed person - 'A person adequately advised or supervised by skilled persons to enable him/her to avoid dangers which electricity may create'.

Ordinary person - 'A person who is neither a skilled person nor an instructed person'.

Socket-outlets circuits:

Now we'll consider the requirements for socket-outlet circuits. Regulation 411.3.3 concerns additional protection, and requires that all socket-outlets in domestic premises be protected by a 30mA RCD - not only those which may supply portable equipment for use outdoors. The wording is that socket-outlets with a rated current not exceeding 20A that are for use by 'ordinary persons' and are intended for general use are to be so protected. The definition of an 'ordinary person' is given above but, however you describe yourself, it includes you. It's intended to cover all who dwell in houses, flats, etc.

The note to Regulation 411.3.3 permits two exceptions:

• Socket-outlets which are under the supervision of skilled or instructed persons, eg. in some commercial or industrial locations, and,
• 'A specific labelled or otherwise suitably identified socket-outlet provided for connection to a particular item of equipment'.

The second exception above could be applied to a socket-outlet which supplies a freezer in a domestic kitchen. It implies that, as long as we have a sign indicating that the particular socket-outlet is for the freezer only, we don't need to have RCD protection for that socket-outlet. Obviously, we don't want the freezer going off because of a temperamental RCD while we're away on holiday. However, the idea that freezers are a frequent cause of RCD tripping is probably somewhat overstated.

Impact protection:

The other matter we must carefully consider at the outset are the requirements of Regulation 522.6.6 and Regulation 522.6.7 regarding impact protection of cables because these Regulations affect the design of the whole installation. Regulation 522.6.6 concerns the protection against impact of cables concealed in a wall or partition at a depth of less than 50mm from the surface of the wall or partition, which is likely to be the case in domestic premises. Regulation 522.6.6 lists measures that can be used to provide mechanical protection for such cables. These are as follows:

1) Use a cable which complies with the requirements of Regulation 522.6.6 (i) for impact protection.

2) Run the cable in earthed steel conduit or trunking or ducting.

3) Provide mechanical protection sufficient to prevent penetration of the cable by nails, screws and the like.

None of these wiring systems looks particularly appealing for domestic premises. Of course, we could always run the cable on the surface in PVC minitrunking. Come to think of it, that's not particularly appealing either. Will any electrician seriously consider installing cables other than 'PVC twin and earth' for domestic installation work? At the present time, I doubt it. While I wouldn't discount the possibility of some type of cable complying with item (1) of the above Regulation being used at some future date, possibly for switch drops, for the purpose of this article, I'll stick with the familiar PVC twin and CPC sheathed cable.

Regulation 522.6.7 requires that, where the installation is not intended to be under the supervision of a skilled or instructed person, and where measures to provide mechanical protection, such as those listed above, have not been applied, then cables must be both:

• Run in 'safe zones' (ie. run horizontally or vertically to the outlet point), and,
• Protected by a 30mA RCD.

The definitions of a 'skilled person' and an 'instructed person' are given above but Regulation 411.3.3 associates electrical installations that are under the supervision of skilled or instructed persons with commercial and industrial locations, not domestic premises.

(Regulation 522.6.8 requires that where a cable is run without adequate mechanical protection in a partition which is internally constructed of metallic parts, then it must be protected by a 30mA RCD, regardless of the depth from the surface.)

The consumer unit:

Having noted the above requirements, we can now discuss how to comply with the 17th Edition. We'll do this by considering three possible consumer unit arrangements which will comply with the new Regulations, although there are other arrangements that could also comply. The reason for demonstrating three arrangements is to show two methods of supplying the fire detection and alarm circuit in new or materially altered dwellings (Figs. 1 and 2), and to show an arrangement which may be suitable when carrying out a rewire in an existing dwelling (Fig.3). In cases of doubt, consult Table 1 in Part 6 of BS 5839:2004 - 'Code of practice for the design and installation of fire detection and alarm systems'.

Fig. 1 shows a consumer unit with two 30mA RCDs and a 30mA RCBO supplying 10 circuits. The fire alarm circuit is protected by the 30mA RCBO. The other four circuits on the left side are protected against overcurrent by four MCBs with additional protection being provided by means of a 30mA RCD. The remaining five circuits are protected against overcurrent by five MCBs and additional protection is provided by the other 30mA RCD. This type of arrangement will 'minimise inconvenience in the event of a fault' as required by Regulation 314.1(i). I've split the circuits as seems reasonable. For example, the downstairs lights are on the same RCD as the upstairs sockets - but not the downstairs sockets. The reason for this is that, if the RCD trips and the downstairs lights go off, the downstairs sockets are still live and you can plug a tablelamp into one of them.

We've mentioned the fire alarm circuit and we'll comment further on it later. For now, we'll discuss the other circuits as appropriate.

Lighting circuits - In the 16th Edition, lighting circuits would not use 30mA RCDs for additional protection because of the possibility of nuisance tripping, leading to the potentially dangerous scenario of people being left in the dark. In the 17th Edition, however, the requirement of Regulation 522.6.7 means that such additional RCD protection applies also to lighting circuits. To eliminate the risk of both lighting circuits going off simultaneously because of nuisance tripping, I've put each lighting circuit on a separate RCD.

The bathroom lighting circuit - Supplementary equipotential bonding may be omitted within a bathroom or shower room where the conditions of Regulation 701.415.2 are complied with. These conditions include the requirement that all final circuits within the location have additional protection by means of a 30mA RCD. The bathroom lighting circuit is supplied by means of a separate circuit, as shown in Fig. 1.

Socket-outlet circuits - This particular freezer is located in the kitchen. I don't fancy the methods of impact protection for my PVC/PVC twin and CPC cable listed in Regulation 522.6.6, nor do I want to run it on the surface, so I've supplied it from the kitchen socket-outlet circuit.

Fig. 2 is similar to Fig.1 but differs in that the fire alarm circuit is protected against overcurrent by an MCB and has additional protection via the adjacent 30mA RCD, which is shared with four other circuits. This may surprise some readers, so I would refer you to the accompanying box article entitled, 'Supplying the fire detection and alarm circuit' for the technical justification.

Fig. 3 again depicts a dual 30 mA RCD consumer unit, but this time, the fire detection and alarm system is not shown because it is not mains-operated. A Grade F system comprising battery-powered smoke alarms has been used. Where existing dwellings are rewired, it is acceptable in the majority of all single-family dwellings to have a minimum system of Grade F (again, Table 1 of BS 5836-6 must be consulted for the full details).

Of course, there are other ways of complying with the requirements of BS 7671:2008 than the methods I've shown in this article. Some will suggest dispensing with MCBs altogether and using only RCBOs. This is a much more expensive option.

Conclusion:

That's it for now. Means of avoiding the need for additional protection by means of a 30mA RCD are likely to emerge. Some will probably be quite ingenious. I expect we'll be discussing the implications of the 17th Edition for some time to come!

In Fig. 2, the fire detection and alarm system, which is Grade D, is wired in PVC/PVC sheathed cable like all the other circuits. It is shown protected by a 6A MCB with the common 30mA RCD providing additional protection. Some may feel that it should be on an RCBO, so I will explain why I have opted for the design shown.

The legal requirement for fire alarm and detection systems in England and Wales is Part B of the Building Regulations 2000. For domestic premises, Part B essentially requires compliance with BS 5839-Part 6:2004 Code of practice for the design and installation of fire detection and alarm systems in dwellings.

Table 1 of BS 5839-6 requires that, for new or materially altered dwellings, the majority of all single-family dwellings (bungalows, flats, maisonettes, two and three-storey houses) must have a minimum system of Grade D (this Table should be consulted for the full requirements). A Grade D system is a system of one or more mains powered smoke alarms, where each alarm has an integral standby supply. Clause 15.5 of BS 5839-6 recommends that the mains supply to smoke alarms and heat alarms take the form of either:

• An independent circuit at the dwelling's main distribution board, in which case no other electrical equipment should be connected to this circuit (other than a dedicated monitoring device installed to indicate failure of the mains supply to the smoke alarms and any heat alarms); or
• A separately electrically protected, regularly used local lighting circuit.

When we compare the recommendations for power supplies for Grade D - as given above - with those of Grade E (see Clause 15.6), we can discern the probable intent of item i. A Grade E system is a system of one or more mains powered smoke alarms with no standby supply. This Clause specifically requires that the RCD protection of smoke alarm circuits in Grade E systems should operate independently of any RCD protection for circuits supplying socket-outlets or portable equipment. No such restriction is made for Grade D systems. We refer again to Fig. 2. Were the common 30mA RCD - which supplies the Grade D fire alarm system - to trip, the internal batteries would operate to ensure the proper functioning of the system. Furthermore, because other circuits would also lose their supply, warning is given that the RCD needs to be reset. This would be especially needful if you went away on holiday for a week or two. If an RCBO were to be used instead, no such warning would be given.

Consequently, the fire alarm circuit, as shown in Fig. 2, does not seem to infringe the likely intent of item i in Clause 15.5 of BS 5839-6, although it is emphasised that the code should be studied to ensure that all relevant recommendations are complied with.

Further information on the requirements of BS 5839-6:2004 for fire alarm and detection systems can be found in articles by Don Holmes in the Competent Person, Number 3, 2007 and Number 5, 2007.

  Simon Clarke, Training Manager at MK Electric, provides his take on the subject, and considers how the role - and usage - of the RCD will change under the new edition of the IEE Wiring Regulations:

MK Electric has produced a video explaining and illustrating the requirements contained in this article; along with information on its 17th Edition Product Solutions concerning consumer unit configurations. The high-quality, informative video is available for viewing, at www.mk.learninglounge.com/resources/sott17esv.html, for other iniatives and solutions please visit www.switchonmk.com

RCDs have been installed in electrical installations for many years, but have become more commonplace since the 14th Edition of the IEE Wiring Regulations, and in its subsequent updates through the 15th and 16th Editions, given the British Standard reference in 1991 of BS 7671 - Requirements for Electrical Installations.

But what is the role of the RCD? Although coming in many guises, put simply its job is to automatically disconnect the electrical supply in the event of fault conditions for protection against fire and harmful thermal effects within installations - such as agricultural premises - but more commonly against Indirect Contact, and for supplementary protection against Direct Contact.

These two definitions have changed with the publication of the 17th Edition in January. Direct Contact will be known as 'Basic Protection' - protection from electric shock under fault free conditions - while Indirect Contact will be referred to as 'Fault Protection' - protection against electric shock under single fault conditions. However it is not only the terminology that will change with the advent of the new edition, as the use of RCDs is set to increase dramatically.

As a necessary safety device, the installation of RCDs has long been required in instances where increased personal protection is required. In domestic situations, this has been to protect socket outlets and other electrical equipment that is intended to be used for outside the home, as well as 'Special Locations': those areas where, for various reasons, increased risk of electric shock is present. These locations include, for example, swimming pools, saunas, construction sites, horticultural premises and caravan parks. These are currently found in Part 6 of the 16th Edition, but will now be found in Part 7, with the new publication being brought into line with the numbering of IEC publications. Part 7 will also include new areas such as marinas, exhibition stands, fairgrounds and floor and ceiling heating systems, where the use of RCDs will be required.

A major change:

And as mentioned above, so as to increase safety, the usage of RCDs is set to increase hugely. Three areas of the Regulations are set to affect them in a major way.

First: Chapter 41 Protection Against Electric Shock. This has requirements for the additional protection of AC systems. Socket outlets with a rated current not exceeding 20A for use for general purposes by ordinary persons, and mobile equipment with a current rating not exceeding 32A for use outdoors are, to be protected by an RCD complying with Regulation 415.1.1, that is a device with a rated residual operating current not exceeding 30mA and an operating time not exceeding 40ms at five times the rated operating current. Exceptions are made for socket outlets under the supervision of skilled or instructed persons, or a specifically labelled or identified socket outlet intended for the connection of a particular item of equipment.

Second: Section 701 Locations Containing a Bath or Shower. This has a requirement for additional protection of all circuits within these areas by one or more RCDs with the previously mentioned characteristics.

But third, probably the largest single impact can be found within Chapter 52 Selection and Erection of Wiring Systems. This includes a number of new and some modified regulations, one of the changes that will have the largest effect can be found in:

522.6.6 - Cables Installed in a Wall or Partition. This says that: 'A cable installed in a wall or partition at a depth of less than 50mm from the surface of the wall or partition shall':

Incorporate an earthed metallic covering which complies with the requirements for a protective conductor of the circuit concerned, the cable complying with BS 5467, BS 6346, BS 6724, BS 7846, BS EN 60702-1 or BS 8436, or;

• be enclosed in earthed conduit, or;
• be enclosed in earthed trunking or ducting, or;
• be mechanically protected against damage, sufficient to prevent penetration of the cable by nails, screws and the like, or;
• be installed in the traditional 'safe zones' - 150mm from the top of the wall or partition or within 150mm of an angle formed by two adjoining walls/partitions, and horizontally or vertically to any point, accessory and switchgear.

A new regulation has been included - 522.6.7 - which covers all circuits. It says: 'Where 522.6.6 applies and the installation IS NOT INTENDED TO BE UNDER THE SUPERVISION OF A SKILLED OR INSTRUCTED PERSON a cable installed in accordance with 522.6.6 (v) (safe zones) and not complying with 522.6.6 (i), (ii), (iii), (iv) (mechanically protected) SHALL BE PROVIDED WITH ADDITIONAL PROTECTION BY MEANS OF AN RCD having the characteristics specified in Regulation 415.1.1' - again by means of a 30mA device.

Domestic installations, and some commercial, will not be under the control of a skilled or instructed person. Final circuit cables would generally be run in the 'safe zones' at a depth less than 50mm; but are unlikely to be installed with one of cable types above or the mechanically protected options given, leaving all final circuits to be protected by a 30mA rated RCD.

However, we must remember the time honoured provision of dividing an installation into circuits to avoid hazards and minimize inconvenience still applies as found in 314.1 (i). Other requirements within this section that will affect the configuration of the circuit protective measures are:
(iii) 'take account of danger that may arise from the failure of a single circuit such as a lighting circuit', and;
(iv) 'reduce the possibility of unwanted tripping of an RCD by circuit protective conductor currents produced by equipment in normal use'.

In essence, consumer unit configuration will change from what is currently the norm. This may be by increased use of RCBOs to provide both residual and over-current protection to individual circuits - a single fault only affecting one final circuit, or by multiple RCDs connected in parallel protecting a smaller number of outgoing final circuits, balancing circuits across these devices such as an upstairs lighting circuit being protected by a different RCD to the downstairs circuit.

Now that the UK electrical industry has finally seen the latest changes to the 17th Edition of the IEE Wiring Regulations (BS 7671), Alan Roadway, Product Manager for ABB's Low Voltage Distribution Products business, explores the new mandatory use of Residual Current Devices (RCDs) and the consequent effects:

An ABB RCD.

The basic function of an RCD is to trip and disconnect the supply of electricity in the event of an earth fault in order to prevent electric shock and fire risk. It does this by detecting the imbalance of currents between the live and neutral lines caused by a fault to earth. Drawing attention to the importance of using RCDs in the right context and with the right equipment, the IEE Wiring Regulations provides guidance on how RCDs should be incorporated in new builds.

One example is the requirement for cables concealed in a wall/partition at a depth of less than 50mm in domestic installations. Such cables will need to be protected by an RCD rated at 30mA or below, even if they are in a safe zone. This has implications for lighting circuits, which - under the still current 16th Edition - have no requirement for RCD protection. Note that both 16th and 17th Editions are run in parallel until full implementation on July 1st 2008, after which all new installations, alterations and additions designed on or after 2nd July will need to comply with the new requirements.

The only exception to this will be if the cables are enclosed in an earthed metallic covering / conduit or equivalent protection capable of resisting nails, screws etc. This is also the case for cables installed in metal-framed walls - a very popular construction technique at the moment.

30mA RCD protection for ALL sockets:

Additionally, all socket outlets rated at 20A or below within a domestic building will require 30mA RCD protection*. This means that all ring main circuits from consumer units will either need to be fed from the RCD side of a traditional split load board or have individual residual current breakers with overload (RCBO) ways.

Because the RCD is sensitive to current imbalances, it is not practical to fit just one device to protect an entire house. If a fault develops within one circuit, all circuits would be switched off immediately. By using individual and grouped RCD protected ways in combination with one another, the required protection can be provided whilst maintaining continuity of supply to other non-affected zones within the installation

Much more detail required:

However, this does mean that, for architects, builders and electricians, much more detail must be put into the design and implementation of any new building supply. Now, utility rooms and storage areas will require specific design and consideration based on the devices installed. Bathrooms are under particular scrutiny. The new regulations will require RCD protection for all circuits supplying electrical equipment within Zones 0, 1 and 2 (Zone 3 is being removed). In addition, all cables buried in walls surrounding bathrooms must have 30mA RCD protection - regardless of the points they are supplying. This could have significant implications on the routing of cables to avoid crossing these zones within ceiling voids and adjoining walls.

Many of the changes to the 16th Edition are part of a harmonisation process to create commonality of installation standards throughout Europe and the world. Whilst the 17th Edition sees an increase in the use of RCDs, it is unlikely that the products themselves will change dramatically as they are have been designed and manufactured to the harmonised and 'normalised' European and worldwide standards in any case.

With more regulations to consider, the IEE Wiring Regulations encourage communications across the industries and enable a more harmonised approach towards building. Now, builders, electricians, designers, manufacturers and our clients will all need to be able to discuss the practices required to meet the new regulations and ensure greater health and safety for any building's inhabitants.

For more information about the RCD options available from ABB, please email This e-mail address is being protected from spam bots, you need JavaScript enabled to view it or call 0800 269 371 to request further information.

Useful electric motor formulas.

Mechanical Formulas.

Torque in lb.ft. =

HP x 5250 rpm

HP =

Torque x rpm 5250

rpm =

120 x Frequency No. of Poles

To Find	Alternating Current
	Single-Phase	Three-Phase
Amperes when horsepower is known	HP x 746 E x Eff x pf	HP x 746 1.73 x E x Eff x pf
Amperes when kilowatts are known	Kw x 1000 E x pf	Kw x 1000 1.73 x E x pf
Amperes when kva are known	Kva x 1000 E	Kva x 1000 1.73 x E
Kilowatts	I x E x pf 1000	1.73 x I x E x pf 1000
Kva	I x E 1000	1.73 x I x E 1000
Horsepower = (Output)	I x E x Eff x pf 746	1.73 x I x E x Eff x pff 746

Symbols

Basic Horsepower Calculations

Horsepower is work done per unit of time. One HP equals 33,000 ft-lb of work per minute. When work is done by a source of torque (T) to produce (M) rotations about an axis, the work done is:

radius x 2 x rpm x lb. or 2 TM

When rotation is at the rate N rpm, the HP delivered is:

HP = radius x 2 x rpm x lb. 33,000 = TN 5,250

For vertical or hoisting motion:

HP =

W x S 33,000 x E

Where:

For fans and blowers:

HP = Volume (cfm) x Head (inches of water) 6356 x Mechanical Efficiency of Fan

Or

HP = Volume (cfm) x Pressure (lb. Per sq. ft.) 3300 x Mechanical Efficiency of Fan

Or

HP = Volume (cfm) x Pressure (lb. Per sq. in.) 229 x Mechanical Efficiency of Fan

For purpose of estimating, the eff. of a fan or blower may be assumed to be 0.65.