Protecting from Backfeed

[Bmell]

Hey guys, I am an apprentice and had a question about protecting yourself from backfeed. After opening the cutout and lifting the hot tap I have seen most guys simply pull (or push up) the hot bug legs on a transformer.

I have also seen some guys shunt the transformer bushings with a piece of #4 CU to protect from backfeed.

Is shunting as safe as pulling the legs? After all, if you pull the legs there is no potential for backfeed.

Also, if you have a bank, either a wye or delta, is it necesary to pull (or shunt) all 3 (or 2 if an open delta) cans?

Thanks...

[Bull Dog]

The rule to live buy is if it aint grounded it aint dead. I dont pull any legs just play it as if its energized unless its grounded then its dead.

[JAKE]

in a delta bank ya gotta kill out all the pots

in a wye you would really have to kill out one to work on it but why only open one?? if you open one phase may as well open all three.

we dont parrellel transformers around here so backfed trans in that situation dosnt happen, its too dangerous to have parrelled trans

as for backfeed from someones generator you could pull the meter or makesure the main disconnect is open

[OLE' SORE KNEES]

Work it Hot or Ground it Out

[scammy]

all of the obove are very correct ,,as for a why bank, you can get up to 20,000 volt backfeed ,,our glove are good for 10, this happend to one of our guys latly ,,also you can blow arestors because of circulating current,that is you repair the bad can ,,and close it in,,,boom,you have to add a temp ground,,,,has anyone else seen this.?

[JAKE]

grounding it out and lifting the grounds before you energize on large wye primary to corner grounded deltas you can get ferrel resonance with large underground feeds.
like scammy said BBOOOOMMM!!

we use 25kv gloves here but we do have alot of 14.4

we had a case of ferrel resoncance a few years back and blew the crap out of the switch gear. pot didnt blow but it did grenade the arrestors. at least they were polymer arrestors and not porcelin grenades.

[Bull Dog]

Arresters can blow anytime any place for any reason. So will the other equipment we work with. Thats what makes this job dangerous. I know of a case were three men were killed in a sub buy a oil switch when they were not even working on anything that caused the explosion. I guess there is some element of fate involved in this job. The very best can and often get killed doing this job. When I was a young app I seen men burned i NEVER thought it would happen to them but it did. Hope we all make retirement and it is much better than the old days.

[australiantroubleman]

We always ground backfeed situations be it a single transformer of a spur line , cheap chinese generators and customers with a "little" bit of electrical knowledge are your worse enemy . It just takes a lead with 2 male plugs and a Tim Taylor type handyman farmer etc and you could be fried .

[Bull Dog]

I did see a article about this handy dandy device that was on sale on the internet. Some bozo was selling it as easy way to hook up generator. All you have to do is unplug your clothes dryer and plug in this thing and your good to go. I think the utilities and government got after him not shure if hes still around lurking out there.

[PA BEN]

We always pull the legs out before we touch the high side.