dave kincaid
Member
I've been hearing that computer circuits should have their own neutrals per circuit due to harmonics upping the ampacity on the neutral any truth to this?or is this a rumor started by a wire salesman!!
neutrals for computer circuits
- Thread starter dave kincaid
- Start date
- Status
- Location
- Massachusetts
Re: neutrals for computer circuits
Dave I will give it a definite 'both', it can be true and the wire people love it.
There are a couple of ways of dealing with it.
You can run separate neutrals for each circuit or you can run a "Super Neutral" which just means an over sized neutral, say Phase A, B, C in 12 AWG with a 10 AWG Neutral. MC cable is available with this super neutral.
Then you get to the panel and it should have a 200% rated neutral bar and a super neutral (usually two neutral conductors the same size as the phase conductors) back to a "K Rated" transformer.
Is any of this really necessary?
I really do not think so, these circuits are never heavily loaded in the first place.
But if the customer wants it and is paying for it the price of the job increases and you should make more profit.
By the way this is only an issue on three phase systems.
Dave I will give it a definite 'both', it can be true and the wire people love it.
There are a couple of ways of dealing with it.
You can run separate neutrals for each circuit or you can run a "Super Neutral" which just means an over sized neutral, say Phase A, B, C in 12 AWG with a 10 AWG Neutral. MC cable is available with this super neutral.
Then you get to the panel and it should have a 200% rated neutral bar and a super neutral (usually two neutral conductors the same size as the phase conductors) back to a "K Rated" transformer.
Is any of this really necessary?
I really do not think so, these circuits are never heavily loaded in the first place.
But if the customer wants it and is paying for it the price of the job increases and you should make more profit.
By the way this is only an issue on three phase systems.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Re: neutrals for computer circuits
I agree with Bob, but also recommend a dedicated neutral and EGC per circuit.
If these are important computers, I don't want the maintenance of one circuit to effect the multiwire neutral or EGC and then disturb the other two circuit's loads.
I agree with Bob, but also recommend a dedicated neutral and EGC per circuit.
If these are important computers, I don't want the maintenance of one circuit to effect the multiwire neutral or EGC and then disturb the other two circuit's loads.
- Location
- Massachusetts
Re: neutrals for computer circuits
That is the one argument against multiwire branch circuits that IMO has merit.
Most times the circuits to 'important computers' are very short anyway (panel in the same room as computers) so it is not a big expense to run separate neutrals.
Now the 'dumb' terminals at every desk are a different story, MWBC all the way.
Oh sure spoil my fun running multiwire branch circuits.
That is the one argument against multiwire branch circuits that IMO has merit.
Most times the circuits to 'important computers' are very short anyway (panel in the same room as computers) so it is not a big expense to run separate neutrals.
Now the 'dumb' terminals at every desk are a different story, MWBC all the way.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Re: neutrals for computer circuits
Ron and Bob bring up good points but I would also consider who is paying for the work. I once bid a job with separate neutrals and one ground per 3 circuits when a customer who was asking for a 'high end' job. Well I didn't get it, but the guy who ran the multiwire BX's did. Seems that the owner didn't want to pay the difference in price after the other contractor convinced him that our system was overkill.
[ October 10, 2005, 08:28 PM: Message edited by: infinity ]
Ron and Bob bring up good points but I would also consider who is paying for the work. I once bid a job with separate neutrals and one ground per 3 circuits when a customer who was asking for a 'high end' job. Well I didn't get it, but the guy who ran the multiwire BX's did. Seems that the owner didn't want to pay the difference in price after the other contractor convinced him that our system was overkill.
[ October 10, 2005, 08:28 PM: Message edited by: infinity ]
Re: neutrals for computer circuits
Here is what I understand
Where you have multiple switching power supplies the 5th harmonic (it is the 5th isnt it) can add up in the common neutral of wye and on the neutral buss in the panel. It is not a problem on the single phase circuits (broken out ?? supplyied by ??) of wye 3 phase
Couple questions on this
1. By separate neutals you guys are saying to use 3 separate neutrals instead of one neutral that si common to 3 receptacle circuits ??
2. If you do not run separate neutrals then you should beef up (# 10 on a 20 3 phase) the common neutral.
Uhhhh why (if that is the case) is this not a problem on edison 3 wire ie 240/120 single phase?
Do the 5th harmonic just cancel on this??
Dan Bentler
Here is what I understand
Where you have multiple switching power supplies the 5th harmonic (it is the 5th isnt it) can add up in the common neutral of wye and on the neutral buss in the panel. It is not a problem on the single phase circuits (broken out ?? supplyied by ??) of wye 3 phase
Couple questions on this
1. By separate neutals you guys are saying to use 3 separate neutrals instead of one neutral that si common to 3 receptacle circuits ??
2. If you do not run separate neutrals then you should beef up (# 10 on a 20 3 phase) the common neutral.
Uhhhh why (if that is the case) is this not a problem on edison 3 wire ie 240/120 single phase?
Do the 5th harmonic just cancel on this??
Dan Bentler
- Location
- Illinois
- Occupation
- retired electrician
Re: neutrals for computer circuits
Don
Yes, the 5th and other odd order harmonics cancel on a 3 wire edison system.
Don
- Status