verification of voltage drop on innitial verification

[shanky887614]

One more question I have is volt drop on three phase. What is the maximum voltdrop on a 400v circuit. 5% would be 20volts. On a question from sparks magazine competition this question came up and the answer was 8volts. I am just wondering where that figure comes from.

edited

 

[shanky887614]

edited

supposed to be 3% for lighting and 5% for sockets

 

[Simonslimline]

Yep happy with 3% on lighting and 5% on other circuits. I mean a 3phase supply to a motor or machine .

 

[shanky887614]

Yep happy with 3% on lighting and 5% on other circuits. I mean a 3phase supply to a motor or machine .

look in onsite guide at table etc, using multiple conductors (poly phase), different cable etc all affect volt drop

ali has higher volt drop than copper for example

cant work it out because dont know length of run

 

[Simonslimline]

What I mean is what is the maximum permissable volt drop allowed to a 3phase 400v motor/machine. This was the question in the sparks competition and the answer was 8volts. I am wondering where the figure comes from as 5% of 400v is 20v and 3% is 12v.

 

[Richard Burns]

Were there any other aspects to the question or was it just "what is the maximum permissible volt drop allowed to a 3 phase 400 V motor/machine"?
I could see that if there were other standards being applied to the equipment rather than just the BS7671 limits that the value of 8 V may be possible, however for a motor one would normally expect them to be more tolerant of voltage drop, particularly on starting up.
8 V is a very tight limit for a motor.

 

[shanky887614]

Were there any other aspects to the question or was it just "what is the maximum permissible volt drop allowed to a 3 phase 400 V motor/machine"?
I could see that if there were other standards being applied to the equipment rather than just the BS7671 limits that the value of 8 V may be possible, however for a motor one would normally expect them to be more tolerant of voltage drop, particularly on starting up.
8 V is a very tight limit for a motor.

depends I was looking through regs and it does mention that there might be a lower max volt drop on motors because of the inrush current.

kind of irrelevant now because of softstarts,vsd's etc

 

[Drexyn]

I was thinking about your question on the 3 phase motor and voltage drop.

My understanding is the maximum value (8V) drop must be across any two phases = (16V) therefore taking in the switchgear into consideration if there was a fault, the motor might still run without realising there is any fault until one of the switches is reset or pressed and systematically opens another circuit.

So the 20V scenario you have worked out may be a maximum permitted value and the 8V would be the actual value across any two phases. I'm hazarding a guess at this mate.

 

[Simonslimline]

Sorry just realised i misread the question. No motor was mentioned. Everyone has answered B. 8 volts. Probably very obvious but i am still confused.




To comply with IEE Wiring Regulations the voltage drop on a three phase 400v Circuit should not exceed:
a) 4v
b) 8v
c) 20v
d) 32v