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#213879 - 08/21/14 10:47 PM Burnt meter leads testing receptacle voltage
Potseal Offline
Member

Registered: 02/23/13
Posts: 189
Loc: Saskatchewan
Today I was in the process of auditing a parkade's receptacles. This 4 level parkade is used exclusively for staff and the receptacles are used during winter months for a vehicle's block heater. While testing a receptacle with an Ideal brand receptacle tester I noticed that one of the indicator lights wasn't as brightly lit as the other. With the model of tester I was using it would show two green lights if the wiring was correct (and that there was power at the receptacle to begin with). At this particular receptacle it appeared that one light wasn't as bright as the other which was something I hadn't seen with the previous. Curious as to why the difference I decided to check the voltage with my Fluke multimeter. First I tested the hot to the neutral and it showed 124V. Next I checked the hot to the ground - bZZZZZ! There was a good flash and I instinctively pulled the leads out. Both meter leads were burnt with the metal tips partially missing. With new leads the meter continued to work fine. Didn't have time to investigate what happened at the receptacle but I decided to check the panel to see what breaker tripped. If the panel was labelled correctly then the breaker didn't trip. I turned the breaker off and marked the receptacle as "Do Not Use". On Monday I will have to investigate what happened but in the meantime I was wondering if anybody has experienced something similar.
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#213881 - 08/22/14 08:12 AM Re: Burnt meter leads testing receptacle voltage [Re: Potseal]
ghost307 Offline
Member

Registered: 05/09/05
Posts: 877
Loc: Chicago Illinois USA
It sounds like you have an open neutral.
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#213882 - 08/22/14 10:03 AM Re: Burnt meter leads testing receptacle voltage [Re: Potseal]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
An open neutral can give you up to 240v nominal (L/N) but that should not blow up a meter. Line to ground should still be ~120v unless the open neutral is on the line side of the service disconnect and MBJ. That would affect all of the receptacles.
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#213883 - 08/22/14 01:56 PM Re: Burnt meter leads testing receptacle voltage [Re: Potseal]
geoff in UK Offline
Member

Registered: 12/30/02
Posts: 170
Loc: UK
To draw an arc which damaged a probe, without damaging the associated meter, suggests to me that you actually touched (and shorted) more than one contact. How this could happen with two probes I can't imagine. However, I also can't imagine a probe-destructive current passing through a meter without damage.

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#213885 - 08/22/14 11:43 PM Re: Burnt meter leads testing receptacle voltage [Re: Potseal]
JoeTestingEngr Offline
Member

Registered: 11/04/05
Posts: 786
Loc: Chicago, Il.
I would suspect that your ground prong connection was damaged in the receptacle, explaining the dim hot to ground indicator. Moving the meter probe around inside could have caused a hot to ground fault, nailing one meter lead. Once the arc struck, the ionized air could've involved the other meter lead. I haven't had it happen to me. Do you recall if the tester had a snug or a sloppy fit in the receptacle?

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#213886 - 08/23/14 09:42 AM Re: Burnt meter leads testing receptacle voltage [Re: JoeTestingEngr]
Potseal Offline
Member

Registered: 02/23/13
Posts: 189
Loc: Saskatchewan
Originally Posted By: JoeTestingEngr
I would suspect that your ground prong connection was damaged in the receptacle, explaining the dim hot to ground indicator. Moving the meter probe around inside could have caused a hot to ground fault, nailing one meter lead. Once the arc struck, the ionized air could've involved the other meter lead. I haven't had it happen to me. Do you recall if the tester had a snug or a sloppy fit in the receptacle?


I don't recall if the tester was loose in the receptacle.

I haven't finished the basic work of going through all the receptacles yet. After the incident with the meter I found a couple more receptacles where the tester gave the same indication regarding the noticeable difference in the indicator lights. I didn't use my meter to test those receptacles since I don't have a 3rd set of leads - haha. Once the initial investigation is done I will have to go back and take a closer look.

Besides the mystery with burnt leads I found an interesting pattern with a run of several receptacles, all in the vertical position, where the top plug tested good and the bottom plug was inconsistent. Inconsistent in that the tester didn't always indicate power in the bottom receptacle until after a second or third attempt or sometimes the right hand indicator light would flicker which, if only one light is showing (left hand side) it means a short to ground. I assume it has to do with the receptacle contacts wearing out but if that's the case why the bottom more so than the top? All receptacles in this parkade are typical duplex style and are shared by two parking spaces and therefore the top and bottom receptacles should wear fairly evenly. Who knows, maybe it's the guy using the tester that's the problem... blush

Initially I thought this job was going to be mind-numbingly boring but instead it has given me a couple things to think about.
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A malfunction at the junction

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#213894 - 08/27/14 07:25 AM Re: Burnt meter leads testing receptacle voltage [Re: Potseal]
Potseal Offline
Member

Registered: 02/23/13
Posts: 189
Loc: Saskatchewan
Here's a pic of the receptacle that I burnt the leads on:



Lot of corrosion, receptacle body falling apart, and the bond wire to the box was badly corroded. A lot of road salt is brought into the parkade on vehicles during the winter months and obviously this takes a toll on the receptacles.


Edited by Potseal (08/27/14 07:26 AM)
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A malfunction at the junction

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#213895 - 08/27/14 11:58 AM Re: Burnt meter leads testing receptacle voltage [Re: Potseal]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
I don't think much testing would be necessary there.
Turn off the breaker, rip out that whole mess and go back new ... with a water resistant cover.
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Greg Fretwell

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#213897 - 08/27/14 02:32 PM Re: Burnt meter leads testing receptacle voltage [Re: Potseal]
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6786
Loc: Brick, NJ USA
Ditto to what Greg said. I would hang an 'unsafe' tag.

IMHO, that has been in bad shape for some time....
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John

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#213899 - 08/28/14 09:08 AM Re: Burnt meter leads testing receptacle voltage [Re: Potseal]
Potseal Offline
Member

Registered: 02/23/13
Posts: 189
Loc: Saskatchewan
That pic was with the weatherproof cover off - I should've mentioned that. They all have weatherproof covers, the majority look the same with cover on, and I had approximately 300 receptacles to test before determining what needed replacing.

Now that I'm replacing receptacles the photo above is what I'm finding. Replacing the receptacles has become a tedious job. Most of the weatherproof cover screws are corroded and are breaking as I attempt to ease them out. This has led to a couple removal methods. Punching them out until I broke a box, cast FS type JB, fortunately at the tail end of a run. Now I'm carefully drilling-out the broken screws and re-tapping. If I do one I figure I might as well do them all. Nothing more frustrating than needing a Robertson AND a blade screwdriver to remove one cover.


Edited by Potseal (08/28/14 09:15 AM)
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