Had a problem at a school a couple of years ago. We had an aprentice go to all the recetacles with the plug-in tester. All rec's showed wiring OK. Most of it was in block work with a 4" sq. box above drop ceiling for termination. There was 120 for power and 277 for lighting. One of the lighting whips was mistakenly tied into the receptacle j.b.. Tester read circuit OK. This tester doesn't tell you voltage. Later on a carpenter plugged in his drill and without even touching the trigger it jumped, spun, smoked and flew out of his hand. I don't know if anything like this ever happened to anyone, but it was a bad mistake, specially in a school.

Thank your lucky stars that they didn't plug one of their new PCs into it.
Luciano, who had been a helper for more than 20 yrs, did the same thing with some 277 travellers. Fortunately, there was no V between them. In Spanish:
Luz=light
ya =still
no = no
Total equation = Still no lights...S

I went to work in a 120/208 Panel in a large building getting near turnover.

Company policy is no live work and I happily shut down the transformer feeding the panel, checked the mains, it was dead.

I started moving some branch conductors around and Blam. Big flash. I checked my self and the coworker with me, we where fine.

What had happened was a 277 lighting circuit got tied into an outlet circuit.

The 120 volt branch breaker had not been turned on so the lighting circuit was working fine along with about 6 277 volt Duplex receptacles.

We commented that at least we found it before someone plugged in a tool, now I know what would have happened if they did

Seriously, now I check all terminals.
Take nothing for granted.

iwire — One more reason it pays to be proficient with a non-contact ac voltage tester. {e.g., Greenlee, Fluke "pen" tester}

Bjarney,
Very true, the company I work for gives them out like candy.

If I am on the clock I have one with me.

The down side, more then once helpers in the company can not seem to remember they do not work on MC etc. Then they cut into live MC.

But they remember after that!

This brings up the problem of mixing voltages on neutral wires. We have got to start identifying our neutrals as well as our hots!

As for the plug-in testers, the only people I see use them are home inspectors by us. Unfortunately, the readings they get with them cost some poor homeowner a service call by me. The results they get just don't seem to be correct very often.

If an electrician can't figure out how to use real testers, they should do some other kind of work. And it doesn't look to professional walking around with one of those either.

I will use one to try and cypher what a home inspector was getting as far as eroneous readings.

If a receptacle had a ground wire from a box tied to the ground screw, and also to the neutral screw, would not the readings be correct on the tester? And no neutral in the box to begin with.

Then comes the voltage issue, real testers will show it is more than 120V.

Now, you folks bring up the issue of lower and higher voltage in incorrect locations. I always make sure that the two shall never meet. 208/120 in it's own runs, 480/277 in it's own runs. Indicating the higher voltage on j-boxes in some locations as a safety precaution for future reference is sometimes nice too.

NonLinearLoad

"This brings up the problem of mixing voltages on neutral wires. We have got to start identifying our neutrals as well as our hots!"

We use gray for 277v neutrals and white for 120v. This is standard practice around here, I just assumed that everyone did this.

And like NLL said, it's better to keep the piping separate. Allthough I will cross systems where necessary to keep the pipework neat.

GJ


[This message has been edited by golf junkie (edited 01-10-2003).]

NonLinearLoad, I might be missing something obvious, but how would "real testers" find the problem you describe any more then the "Snake Eyes" tester.

I have a few different meters and "wiggys"
But I always have a receptacle tester it's fast and efficient when checking large numbers of outlets. Luckily 277 volts at the receptacle is rare.

And on the keep it separate, well that would be the intent

I think where the problem is as first mentioned, it was a whip that tied into a rec. j.b.. There was a lighting j.b close and the two whips were crossed. All the conduits were separated, the J.B.s were all marked for circuits and voltages. But all the M/C looks the same. Is there M/C available where the outer jacket is colored to signify voltage? This has only happened once that I've seen or heard about.

Wirenuttt, there is new MC cable that has brown/orange/yellow markings on the jacket for 277/480.

try here Ange......

I'm glad that using grey wire for 277v. neutrals was mentioned...As I read the 2002, this is no longer allowed! (One of the things I don't like).
This is a broader subject, however. When you "share" neutrals between circuits, it can be difficult at the panel to identify the other circuits that share a neutral.
When you are running isolated ground circuits for data processing circuits, it makes sense to have separate neutrals for each circuit, so that there are fewer ways for one circuit to "dirty" the power on another circuit.
I expect that marking our wires, etc., will become even more important with time.

John,
Why can't you use grey for 277 volt neutrals? Please cite the section. Thanks.
Don

iwire,

The rec't. scenario I mentioned was just throwing out "what-if's". And, no you could not detect any difference with any tester.

But, I have had homeowners see a apprentice using the plug-in and ask why. Then the assumption on their part is that is the only thing they need to be a pseudo electrician was the plug-in to do electrical inspections.

I have had quite a few 2 year apprentices come on board that have no clue as to how to use a "wiggy", or any other kind of tester for that matter. Now I have suspicions as to whether they actually tested the devices I wanted tested.

We would start guys out with voltage meters only, then they could graduate into a continuity tester. This is always a challenge for them as well as myself.

You gotta admit though, we all look really COOL with a used "wiggy" hanging around our necks, official and all, yea, a JOURNEYMAN kinda COOL!

Sorry for the rec't banter!

NLL

I am surprised the lites in the plug in tester did not blow out from the 277 voltage.

spyder; That's just the point, the tester is rated for 600 volts.
~Ange
ct and sparky, thanx

NLL, you can't beat the look of the wiggys!

The company I work for goes the oppisite way on testers, helpers are not allowed to do testing with meters, (I know, don't jump on me I did not make the rule) The company considers this live work.

On a side note someone should make a plug in tester with audable voltage warning.

Below say 110 or above 125 and it would make a noise.

Bob

whoa!...no more gray neutral wires on 277v.?
hmmmmmm....if thats true, then i got about a million feet of gray wire i'll sell real cheap!.....:S......say it aint so!!!!

The only references I can find to the "grey" wire is that conductors larger than #6 cannot be field identified at the terminations with grey, but must use white...and that's not new.
Also, there's a FPN that warns of the use in the past as an ungrounded conductor.(although I can't find any prohibition of its use as such in the present)
The word "natural" (as in natural grey) was removed.

Oops! I goofed!
I recalled (correctly) that the 2002 code no longer mentions "natural grey". I failed to recall that it now says only "grey" instead. So yes, grey -even unnatural grey- is OK for neutrals.
Anybody know a place that serves crow?