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#61937 - 02/06/06 03:54 PM Voltage Drop on Neutral  
Specialty  Offline
Junior Member
Joined: Jan 2006
Posts: 4
Lake in the Hills,IL
We are supplying (120v) 2000VA of parking lot lights 130' away. The foreman ordered #10 pulled. The boss questioned the #10 and recomended adjusting ungrounded conductor to #8 for voltage drop (the foreman agreed). There is sufficient ampacity in the 10's, so does the #10 neutral also need to be replaced with #8, or just the hot since we don't care about voltage drop going to ground?


John

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#61938 - 02/06/06 04:43 PM Re: Voltage Drop on Neutral  
gfretwell  Offline


Member
Joined: Jul 2004
Posts: 9,097
Estero,Fl,usa
Voltage drop doesn't care if it is coming or going, they add. You should make the neutral the same size as the ungrounded conductor. It might be argued that in a multiwire the neutral would not need to be any bigger than the 240.4(D) requirement since if the load was balanced it would not carry any current at all. If this is just a single circuit it carries the same as the ungrounded wire.


Greg Fretwell

#61939 - 02/06/06 04:55 PM Re: Voltage Drop on Neutral  
jfwayer  Offline
Member
Joined: May 2005
Posts: 30
Fairmont, WV, USA
Electricity needs a complete path, from source to load, through load, from load back to source. This involves both the hot and the neutral or grounded conductor.

The current (I) is 2000VA/120V or 16.67A

The resistance of #10 is 1.21/kFT and #8, .764/kFT (NEC table 8)

120FT of #10 is 120 * 1.21 / 1000 = .146ohms
120FT of #8 is 120 * .764 / 1000 = .092ohms
The voltage drop comes from the resistance of the hot wire and the neutral.

The voltage drop for 120FT #10 is 16.67 * .146 = 2.43V
The voltage drop for #8 is 1.53V

#10 neutral and hot is 2.43 + 2.43 = 4.86V
#8 neutral and hot is 1.53 + 1.53 = 3.06V
one #10 and one #8 is 2.43 + 1.53 = 3.96V

3% of 120V is 3.6V, so both #8 is ok, one #8 and one #10 is marginal, and both #10 is poor.


If the load is distributed (or the circuit is 120/240V) the analysis is different.


JFW

#61940 - 02/06/06 05:42 PM Re: Voltage Drop on Neutral  
John Crighton  Offline
Member
Joined: May 2005
Posts: 177
Southern California
Another issue: Is an EGC being run with the circuit? If you oversize the conductors for voltage drop, you need to oversize the EGC by the same amount.


#61941 - 02/06/06 06:09 PM Re: Voltage Drop on Neutral  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
As John C. brought up the EGC is required to be increased in size if you increase the circuit conductors.

In this case we can assume this is a 15, 20 or 30 amp circuit all of which require a full size EGC.

If you run 8 AWG for the 'hots and neutral' you will have to run a 8 AWG EGC to comply with 250.122(B).

In my area inspectors are sharp on this and will catch this if you ignore it.


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#61942 - 02/06/06 06:39 PM Re: Voltage Drop on Neutral  
Specialty  Offline
Junior Member
Joined: Jan 2006
Posts: 4
Lake in the Hills,IL
You guys are great, thanks for your help in confirming what we suspected. The poles are required to be grounded directly so the EGC is not at issue.

Thanks Again


John

#61943 - 02/06/06 06:43 PM Re: Voltage Drop on Neutral  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
Quote
The poles are required to be grounded directly so the EGC is not at issue.


Please explain what you mean.

Some sort of EGC absolutely must be run with the circuit conductors back to the panel.

It could be a metal raceway or a conductor but one or both must be used.


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#61944 - 02/06/06 06:46 PM Re: Voltage Drop on Neutral  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,851
Brick, NJ USA
Specialty:

What do you mean.."You guys are great, thanks for your help in confirming what we suspected. The poles are required to be grounded directly so the EGC is not at issue"

Some specs require a driven grd rod at each pole...this however is in addition to the EGC that you run with the circuit.

I'll second or third what the other esteemed members stated regarding the EGC upsizing, and increasing the neutral conductor.

John


John

#61945 - 02/06/06 07:13 PM Re: Voltage Drop on Neutral  
walrus  Offline
Member
Joined: Jul 2002
Posts: 680
Bangor Me. USA
CAn anyone explain the use of a ground rod at each pole?? Lightning protection?


#61946 - 02/06/06 07:43 PM Re: Voltage Drop on Neutral  
Roger  Offline
Member
Joined: May 2002
Posts: 1,716
N.C.
Walrus, lightning protection and/or a HV event is the only reason for the rod.

Specialty, Welcome to the forum.

Now, the individual pole grounding will not protect the pole, light, or people from a fault, and infact without a EGC it can add to the dangers in the way of dangerous voltage gradients around the rod in a fault condition.

You MUST install an EGC for people safety. This is non negotiable.

Roger


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