63a tp&n

[wmb1973]

Hi everyone,

When calculating for a 63a tp&n supply (SWA) do you do each phase as a third of 63a ie 21a per phase or 63a per phase (3*63a Breakers) for V.D., cable size etc.

Thanks in advance for your help.

 

[Davey101]

63 per phase mate. If its a 63 amp supply, then its 63amps, doesnt matter if its 1,2 or 3 phase.
Edit-is it actually 63 amps per phase, or just fed from a 63 amp mcb?
Somebody (much) better at design will be able to give you a technical answer

 

[Guest123]

Hi

If your 63A MCB is for protecting a sub-main to another DB for instance then there is the potential for the full 63A to be drawn on each phase, depending on if there are balanced 3 phase loads or lots of single phase loads. The cable must be selected having taken all circuit parametrs and installation factors into account, to carry the full 63A on each conductor if this is the case.

 

[offshorealex]

cable size does not need to be as large for a 3 phase 63a supply as it would be for a single phase.(depending on the usual length of run temp etc factors) A 63 amp 3 phase supply will provide 3 single phase supplies at 63a.

 

[wmb1973]

This is for a 63A TP&N Lift supply.

 

[MarcT]

how long is the run?

 

[wmb1973]

@20m run using SWA (Cleated to wall)

 

[mjvor]

Hi everyone,

When calculating for a 63a tp&n supply (SWA) do you do each phase as a third of 63a ie 21a per phase or 63a per phase (3*63a Breakers) for V.D., cable size etc.

Thanks in advance for your help.

WMB - Your lack of understanding of 3 phase is frightening me. Have you been asked to select and install a suitable cable for a 63A lift supply? There are several factors to consider including earth loop impedance, discrimination, volt drop as well as current carrying capacity/ grouping etc. Please get professional help. A lift is for the public and legally they are entitled to better than informal design help from well meaning forum members who can't possibly know all the factors. Have you ever terminated a SWA before? If not, don't practice on the public!

 

[IP4X]

This might help understanding 3 phase.

For the three phase the power calculation is:
P=root3 x V x I x CosO

CosO is the power factor depending on the load capacitance or inductance.

Assumung unity power factor:

P = 1.732 x 400 x 63 x 1
= 43647.68W

For single phase calculation:

P = VI
P = 230,94 x 63
= 14549.2 W
Which if you multiply by 3, as you have 3 individual phases you get

P = 43647.68 W

So the current is the same! 63A!

So dont divide your amps by 3.

Cheers

 

[wmb1973]

Hi IP4X, have you ever wired a missile or aeroplane engine ? No i doubt it. and if you wanted to ask me question about doing so i wouldn't start fretting about flying in the near future. I am asking a question about selecting a cable on paper, not thinking of wiring in. Even though i'm fully qualified to do so. Thanks IP4X.

 

[IP4X]

Hi wmb1973
Not too sure bout your reply there?
I just wanted to use a quick example to show that a 63A three phase supply will have, at full load 63A, flowing in each line ( at different phase angles 120 degs apart ). which would affect your calculations.I used the power calculation as I assumed you were confusing the relationships of power and current in single/three phase calculations.
If ever someone mentions 63A three phase, they mean 63A is the line current value.
Cheers

IP4X (after a night on the fosters)

 

[MarcT]

WMB - Your lack of understanding of 3 phase is frightening me. Have you been asked to select and install a suitable cable for a 63A lift supply? There are several factors to consider including earth loop impedance, discrimination, volt drop as well as current carrying capacity/ grouping etc. Please get professional help. A lift is for the public and legally they are entitled to better than informal design help from well meaning forum members who can't possibly know all the factors. Have you ever terminated a SWA before? If not, don't practice on the public!

Do you feel better now?

 

[mjvor]

Do you feel better now?

No.

A lot of questions (and the answers) on this site scare me. I've been in this business 40 years and I've seen a lot of the bad bits. They're not nice and it's turned me into a grumpy old man.

 

[MarcT]

I totally get that.

 

[Guest123]

Thread Closed.