 tschmidtPremium,MVM
join:2000-11-12
Milford, NH
kudos:8
 ·G4 Communications
·Fairpoint Commun..
 ·Hollis Hosting
| reply to Jack_in_VA
Re: Electrical Insanity said by Jack_in_VA: If the load is balanced between the two hots you don't even need a neutral. That is absolutely correct. However loads are never exactly matched, if neutral integrity is compromised Neutral is no longer at 0 volts relative to local Earth but at higher value depending on the degree of imbalance. Worst case, compared to your best case, is no load on one leg. In that case Neutral will be 120 volts above ground.
Typically, Earth resistance is relatively high so ground electrode will not do much to reduce neutral current. In an urban area substantial current will be carried by the water system, assuming it is metallic, creating a shock hazard to utility workers working on the system.
/tom |
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 AVDRespice, Adspice, ProspicePremium
join:2003-02-06
Onion, NJ
kudos:1 | said by tschmidt: In an urban area substantial current will be carried by the water system, assuming it is metallic, creating a shock hazard to utility workers working on the system.
/tom
citation? |
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 nunyaWho is John Galt?Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:8
 ·Charter
·surpasshosting
| He really doesn't need a citation. It's the basic laws of physics. The water utility workers could be exposed to the un-intentional current on the water pipes if they "open" a segment.
Ordinarily the unintentional current from an open neutral would travel through the water pipe to the adjoining neighbors bond and back the MGN. You don't want to have your paws in that broken path.
That's why we jump water meters too.
Some water utilies carry a bonding cord, but I'd be willing to bet it rarely gets used. Same thing happens with CATV and Telco as well on a greater extent. Their sheaths unintentionally carry the current of the MGN. If the power MGN is defective, that puts the entire load across the other utilities attached to the MGN. I've seen this a few times 1st hand.
But if you want a diagram...
»ecmweb.com/nec/code-basics/2011-···0110601/
--
I just might be the most "licensed" S.O.B. you know.
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sk1939Premium
join:2010-10-23
Washington, DC
kudos:9 | Open neutral causing neutral to flow through CATV line:
»www.electrical-forensics.com/Ope···ral.html |
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