Circuits for Motors- how to in the UK?

[Megawatt]

Cookie I passed the masters test, who are you trying to teach. I don’t need Mike Holts information I already know it i have wired , sized , installed 3 phase motors for 33 years. I guess Mike Holt is wrong you use the current the code book gives you not the nameplate. You have a lot to learn. Quit quoting the code book to me on stuff I already know
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Cookie you are just reading a book, I’m telling you with out a book, I already know the code that’s why I’m a master and your not
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This topic is over it’s a UK forum so quit boring everybody

Since you are in article 430 let’s say you have a 20 hp 3 phase 6 lead continuous duty motor what size wire does it require and what size maintenance disconnect does it take
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Nobody said they did, the OP has asked how we size the cables.

Nobody cares how you size cables

 

[davesparks]

Nobody cares how you size cables

Well that's just plain rude!
Somebody does care how we size cables, the OP, that was the whole point of them starting this thread!

You should wind your neck in.

 

[Cookie]

Cookie I passed the masters test, who are you trying to teach. I don’t need Mike Holts information I already know it i have wired , sized , installed 3 phase motors for 33 years. I guess Mike Holt is wrong you use the current the code book gives you not the nameplate. You have a lot to learn. Quit quoting the code book to me on stuff I already know
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Cookie you are just reading a book, I’m telling you with out a book, I already know the code that’s why I’m a master and your not
[automerge]1575413010[/automerge]

This topic is over it’s a UK forum so quit boring everybody

You are correct in terms of sizing wire- you use the code. In terms of setting overload protection you use the nameplate on the motor. I doubt Mike Holt is wrong, certainly not on something so basic.


I'm quoting code because on black and white it vindicates my assertions.


I'm curious to hear from the UK guys on how they would do a motor install. Especially with type B, C, and D MCBs to choose from.

 

[Cookie]

Since you are in article 430 let’s say you have a 20 hp 3 phase 6 lead continuous duty motor what size wire does it require and what size maintenance disconnect does it take
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Nobody cares how you size cables

125% of 54 amps (230 volts) = 67.5 amps

125% of 27amps (460 volts)= 33.75 amps

Assuming 3 wires in conduit and 75*C terminations we get:

#4 (21.15mm2) copper at 230 volts

#10 (5.26mm2) copper at 460 volts


For 60*C terminals:

#4 (21.15mm2) copper at 230 volts

#8 (8.37mm2) copper at 460 volts

I'd put the 230 volt unit on 100amp disco and the 460 volt unit on a 60amp disco as 30, 60 and 100 are standard sizes.

 

[ElectroChem]

For a single motor supply circuit here in Australia I would size the overload protection to the FLC from the motor nameplate. (There are a couple of regs around which motors do and don't need overload protection).
Then the circuit protection would be the next size up from there i.e. a 7.6A FLC motor would need at least a 10A supply, possibly with a D-curve breaker if it's a heavy starter.
Cable would then be sized to the supply based on the standard tables in AS3008 or calculated from scratch (rarely). Rules of thumb are also common like using 2.5mm for smaller circuits in industrial settings.

 

[Lucien Nunes]

90 degree 2 phase is not something we've ever had here and it is always nice to learn something.

I think we have used it here historically in a couple of supply systems, I would have to look it up. IIRC there were two implementations, one used equal sized supplies and symmetrical motors, the other used a lower-rated 'teaser' phase with 1-ph load always on the main phase.

I always cringe when people call a circuit using two line conductors from a 3-phase supply '2-phase' as it's often more trouble than it's worth to explain why it isn't!

 

[Lucien Nunes]

I find it quite odd that you would look up a current rating in the book based on HP rather than using the FLC of a motor.

I believe the logic, and perhaps Cookie can comment, is that the circuit (which is not adjustable after installation) should be sized to allow sufficient ampacity for any standards-compliant motor of that power that might be fitted now or in the future, that might have a marginally different FLC compared to the one specced at installation time. But the overloads are set according to the particular motor in use, based on nameplate FLC.

 

[Cookie]

I believe the logic, and perhaps Cookie can comment, is that the circuit (which is not adjustable after installation) should be sized to allow sufficient ampacity for any standards-compliant motor of that power that might be fitted now or in the future, that might have a marginally different FLC compared to the one specced at installation time. But the overloads are set according to the particular motor in use, based on nameplate FLC.

You got!

The code mandates larger wire in the event the new motor coming in has a higher FLC. Also, HVAC techs, electricians and maintenance guys are always told to re-adjust the motor overloads when replacing an old motor with a new one. Its common to forget.

 

[Cookie]

I think we have used it here historically in a couple of supply systems, I would have to look it up. IIRC there were two implementations, one used equal sized supplies and symmetrical motors, the other used a lower-rated 'teaser' phase with 1-ph load always on the main phase.

I always cringe when people call a circuit using two line conductors from a 3-phase supply '2-phase' as it's often more trouble than it's worth to explain why it isn't!

If you look at old power lines that are still in service in US cities you can even see the remnants of 2 phase power. Often the cable riser pot will have 4 bushings and a 4th insulator (without a conductor in it) on the cross arm or the cross arm with have insulator pins in multiples of 4 instead of 3. The 2 phase was abandoned and changed to 3 phase decades ago but the old stuff remains.

HELCO 4.8kV - East Hartford, CT

By Power Lines. Here's a pretty old riser pole that looks to be a possible remnant of HELCO's long gone four-wire two-phase distribution system (which also ran at 4.4/4.8kV as well). Note the four ter…

www.ipernity.com

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Here is a pic I took of one of those poles 10 years ago:
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Only the pic to the right is mine, the one on the left is AR's from Ipernity.

 

[Cookie]

2 Phase power was mentioned in this thread. Here is post where a US electrician is replacing it in a US installation.

3 phase and 2 phase in the same system

Would this be a viable system? Is this called a Taylor system? Does the scott-T autotransformer do any phase displacement or shifting? Could a neutral be added for the 3 phase?

forums.mikeholt.com

2 phase power does still exist in select locations throughout the US.