How to calculate how much volt drop % is already used?

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JamieP
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How to calculate how much volt drop % is already used?

Post by JamieP »

Is there any good suggestions or easy ways on how you choose to work out what % of VD from the PoS to the point you install from is?

For example, main switchboard in a home isn't too bad because you can usually roughly calculate mains length to where the MSB is

However, in a large factory with multiple DBs all over the place, what ways do people use to calculate what they have left to work with?
AlecK
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Re: How to calculate how much volt drop % is already used?

Post by AlecK »

I am not aware of any easy way to determine the available margin of VD with any sort of accuracy.
We can assume % for mains, & for submains, etc, but it can't be anywhere near accurate.
And VD is a "must never exceed" limit.
I believe it should be a requirement to record, at every switchboard, the size & route length of the conductors supplying it.
Still need to establish load for each swbd - max demand is probably OK for this.
JamieP
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Re: How to calculate how much volt drop % is already used?

Post by JamieP »

I agree about recording the size and length, it's vital information in determining these things

I've never found a good way other than an educated guess, which can be easier in small domestic installations but increasingly difficult in large complex installations with multiple distribution layers. Just wondering I by chance someone else had some good tips or tricks.

In saying that, I've never seen a real world situation of it being an issue despite the fact almost no one seems to know the value of allowence when specing things.
AlecK
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Re: How to calculate how much volt drop % is already used?

Post by AlecK »

I think not so much that everyone complies;
most give it almost no thought.
But nobody gets caught
Slovett
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Re: How to calculate how much volt drop % is already used?

Post by Slovett »

A method I've been told about and use is to use a loop impedance tester. However it does require taking a reading from the PoS, which usually means you need to get the Network involved for access.

Comes in handy if you are trying to fix Voltage Drop issues that may be within an Installation.

Example - A reading of 0.29ohms at the the PoS - then a reading of 0.38 ohms at the Main SwitchBoard.
0.38ohms - 0.29ohms = 0.09 ohms between PoS and Main SwitchBoard
If we assume the Mains have been calculated for what ever Overload protection is protecting the Mains ie 63A
Then Ohms Law V=I.R
V= 63A x 0.09 ohms = 5.67 Volts

5.67V / 230 = 0.0247
0.0247 x 100 = 2.47% Vold Drop @ 63A
AlecK
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Re: How to calculate how much volt drop % is already used?

Post by AlecK »

Agree using difference-in-loop-impedance as described would give a usable figure for VD in mains;
based on MD by limitation at rating of supply fuse.
Could do similar for any submains (A-N, rather than A-E as for EFLI).
By using the overcurrent device ratings as the MD, will be on the safe side - and saves a lot of calculation.
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