5 % rule

[normbac]

Is 5% maximum the general rule for voltage drop allowance am running 2oo ft to a 100 amp sub from a 200 amp house main is #2 ok tia

 

[hey_poolboy]

Re: 5 % rule

You are correct in that 5% is the "rule".
A number of online voltage drop calculators are available. I thought there was one in the "Free Stuff" link on Mike's home page, but I couldn't find it. I know there are a couple at Electrician.com Just plug in your details and it will figure the VD for you and or correct the wire size.

Mike

 

[iwire]

Re: 5 % rule

It is more of a suggestion than a rule.

Conductors for branch circuits as defined in Article 100, sized to prevent a voltage drop exceeding 3 percent at the farthest outlet of power, heating, and lighting loads, or combinations of such loads, and where the maximum total voltage drop on both feeders and branch circuits to the farthest outlet does not exceed 5 percent, provide reasonable efficiency of operation. See 215.2 for voltage drop on feeder conductors.

 

[dereckbc]

Re: 5 % rule

Originally posted by normbac:
Is 5% maximum the general rule for voltage drop allowance am running 2oo ft to a 100 amp sub from a 200 amp house main is #2 ok tia

No it is not enforcable.

 

[charlie b]

Re: 5 % rule

I just ran a quick check. If this is a single phase, 120/240 volt system, then a #2 will give you about 3% VD. But you should download a calculation spreadsheet and run it yourself, just to become familiar with the process.