# Backfeed



## Cletis (Aug 20, 2010)

If you just use a tic tracer you'll never get shocked with backfeeds


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## bmart (Dec 28, 2011)

I own and use my Tic Tracer. Make sure you are on the right scale. It does pick up motor and TV magnetic fields,and could be misleading.


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## dmxtothemax (Jun 15, 2010)

Two things must be done to assure maximum safety !

1 - Assume it's live until tested and proven otherwise !
2 - Put a ground jumper on ALL incoming lines !


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## Big John (May 23, 2010)

A friend of mine was almost killed by a backfeed. During a system outage someone scabbed a generator into an existing 480V circuit without isolating it. Of course it re-energized everything ahead of that circuit as well, back up through the step-down transformer and into the switchgear cubicle where my buddy was working. He touched the bus bar and got the business end of 12,470.

I've talked to guys who were there with him and they said he had smoke rolling off him. The guy who scabbed in the generator said he didn't know electricity could go the other direction. 

There's a lot to be said for applying safety grounds, and it ain't dead until it's grounded, even on low voltage equipment.


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## dmxtothemax (Jun 15, 2010)

Big John;1082991 The guy who scabbed in the generator said he didn't know electricity could go the other direction. [/QUOTE said:


> I surrpose that there is some ignorance out there !
> But would the linesmens family/wife accept that excuse !
> Me thinks not !
> 
> ...


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## RHWilks (Jul 14, 2012)

I got the p!ss nailed out of me during the okc 2007 ice storm. Poco said bug in if the drop was dead. I was connecting, bare handed.. (I know stupid. I checked the drop and it was dead) I was making up the last connection, I hear a generator start. I got lit up!


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## dmxtothemax (Jun 15, 2010)

Well a ground jumper would have stopped that happening !

Did you learn the lesson ?


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## macmikeman (Jan 23, 2007)

I have carried the same length of chain around for probably 25 years now. Chain goes around A,B, C, and neutral on shutdown, stays locked on till I am done and off the bus. This was repeatedly stressed to us in vocational school dozens of times.


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## RHWilks (Jul 14, 2012)

dmxtothemax said:


> Well a ground jumper would have stopped that happening !
> 
> Did you learn the lesson ?


Yep, ground it or ppe up.


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## bmart (Dec 28, 2011)

I was checking out a high rise electrical vault that lost power in the main line 12 KV vault due to a flood. The water engulfed the 7.2 kv/120v pot transformers and flashed over. I arrived 10 seconds after an employe received an electrical shock and was carried out of the switchgear cubicle and to the floor. He never recovered. Backfeed was applied with test leads from a temporary power source to test the ATO switchgear controls. The 120V was installed on the line side of the operating bus and stepped up to 7200 volts. The mechanic was in cubicle cleaning the equipment. Unfortunately, the pot transformer connection was disconnected from the grounded line!


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## guest (Feb 21, 2009)

macmikeman said:


> I have carried the same length of chain around for probably 25 years now. Chain goes around A,B, C, and neutral on shutdown, stays locked on till I am done and off the bus. This was repeatedly stressed to us in vocational school dozens of times.


I will try to find the source of this next comment again and link to it or quote it fully, but it has been said that chains are NOT a safe or often effective grounding rig. Why? Because the multiple contact points between the links cause arcing that can lead to a serious flashover. 

A POCO style grounding rig is, in the grand scheme of things, not that expensive and is infinitely safer than using chains. 

This set is available at Grainger's (at their typically high price of course) 

http://www.grainger.com/Grainger/SALISBURY-Four-Way-Grounding-Set-5ZV74?Pid=search

but candidly, even at that price it is still a lot cheaper than the hospital bills from an arc flash/electric shock incident....and as work equipment it is tax deductable.


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## Big John (May 23, 2010)

No mistake, I think the chain is better than nothing, for sure. But my understanding is that during a severe enough fault the chain links look like a ton of high-impedance connections. They increase the fault clearing time in addition to heating up and spraying molten metal everywhere.

If you're gonna ground like that, maybe switch to a piece of finely stranded 4/0 instead?


bmart said:


> ...Backfeed was applied with test leads from a temporary power source to test the ATO switchgear controls. The 120V was installed on the line side of the operating bus and stepped up to 7200 volts. The mechanic was in cubicle cleaning the equipment. Unfortunately, the pot transformer connection was disconnected from the grounded line!


 That's terrible. In the story I told, the yokel who connected the generator was just some contractor, not a sparky, and only knew enough to be dangerous. But anyone doing gear testing I would expect to full well understand the risks of backfeeding.


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## GEORGE D (Apr 2, 2009)

Wow guys, another wake up call for me on how behind I seem to be with safety. I do recall years ago when working for some outfit, we were doing PM's on switchgear and PC used that ring in transformer when they shut down for us. If one were to make one, what minimum size would you recommend and any advise on how/what material?


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## KDC (Oct 19, 2012)

It depends on the fault current & duration. the Poco I work for uses a mix of #2, 2/0, 4/0 and 2 parallel 4/0 cables, depending on where the work's getting done.

That said, it's a safety device, and should be treated at such. Manufactured to specs, tested on a schedule. 

The proper cable and clamps aren't cheap. We're looking at replacing a bunch of ours and the current diy price estimate is $40k.


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## GEORGE D (Apr 2, 2009)

KDC said:


> It depends on the fault current & duration. the Poco I work for uses a mix of #2, 2/0, 4/0 and 2 parallel 4/0 cables, depending on where the work's getting done.
> 
> That said, it's a safety device, and should be treated at such. Manufactured to specs, tested on a schedule.
> 
> The proper cable and clamps aren't cheap. We're looking at replacing a bunch of ours and the current diy price estimate is $40k.


Holy shiitake mushrooms, I think I'll just get electrocuted instead. In all honesty I plan on utilizing something when in this scenario again.


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## guest (Feb 21, 2009)

KDC said:


> It depends on the fault current & duration. the Poco I work for uses a mix of #2, 2/0, 4/0 and 2 parallel 4/0 cables, depending on where the work's getting done.
> 
> That said, it's a safety device, and should be treated at such. Manufactured to specs, tested on a schedule.
> 
> The proper cable and clamps aren't cheap. We're looking at replacing a bunch of ours and the current diy price estimate is $40k.


See post #12.:whistling2:



GEORGE D said:


> Holy shiitake mushrooms, *I think I'll just get electrocuted instead. In all honesty I plan on utilizing something when in this scenario again.*


See post #12. :whistling2:


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## dmxtothemax (Jun 15, 2010)

Something like this could work on 120/240 stuff,
I wouldnt use it on KV type stuff.

View attachment 28516


Safety Cletis style !


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## chewy (May 9, 2010)

dmxtothemax said:


> Something like this could work on 120/240 stuff,
> I wouldnt use it on KV type stuff.
> 
> View attachment 28516
> ...


Thats what my dads friend told me, "If your ever working on something jumper it up so it blows up in the assholes face when he turns it on".


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## guest (Feb 21, 2009)

dmxtothemax said:


> Something like this could work on 120/240 stuff,
> I wouldnt use it on KV type stuff.
> 
> 
> ...




Ummmm, no. :no::no::no:

Those clamps do NOT have enough grip strength and WILL blow right off of the lugs/bars/conductors under a fault. 

And I do not believe the cable is rated for anything over 50 volts anyway.


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## swimmer (Mar 19, 2011)

......................


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## swimmer (Mar 19, 2011)

Cletis said:


> If you just use a tic tracer you'll never get shocked with backfeeds


I can't believe I "Thanked" Cletis for something:laughing:


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## swimmer (Mar 19, 2011)

swimmer said:


> Question to all: Anyone try a voltage ticker on DC? I've got a 30V power supply in the garage. Think I'll give it a try and let you know.


Apparently, my Klein Cat IV alarms for 30VDC


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## Big John (May 23, 2010)

_Swimmer,_ be careful,I don't know of any tic tracer that can function on true DC. They pick up a changing electric field, and the field around DC is usually static. Maybe the DC you picked up had a ton of ripple?


mxslick said:


> ...Those clamps do NOT have enough grip strength and WILL blow right off of the lugs/bars/conductors under a fault...


 I agree, there's a chance of that happening.


> ...And I do not believe the cable is rated for anything over 50 volts anyway.


 But grounds don't need a voltage rating.


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## swimmer (Mar 19, 2011)

Big John said:


> _Swimmer,_ be careful,I don't know of any tic tracer that can function on true DC. They pick up a changing electric field, and the field around DC is usually static. Maybe the DC you picked up had a ton of ripple?


So now I have to put an O-scope on the power supply?
It's really an electroplater given to me by a customer.
I'll let you know what I find if I ever do it.


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## Big John (May 23, 2010)

swimmer said:


> So now I have to put an O-scope on the power supply...?


 Check for pulsed DC by measuring Hz in DC mode. Also try switching it over to AC: If you have ripple, it'll show up.

Wasn't trying to bust your balls, just an FYI.


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## KDC (Oct 19, 2012)

mxslick said:


> See post #12.:whistling2:


The phrase "not big enough" comes to mind. 

We're replacing multiple sets built with 4/0 that are 10' to 25' long, with clamps that have to fit (easily) on 5" round buswork. 

I currently work in a HVDC converter station. Not you're standard application. :laughing:


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## Big John (May 23, 2010)

KDC said:


> ...I currently work in a HVDC converter station....


 And you're not posting pictures for us?!


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## bmart (Dec 28, 2011)

The Tif 300 HV Tic Tracer states on the device: "Test unit on a known *AC* conductor."


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