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.

It sounds like you have an open neutral.

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.

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.

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...

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

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.

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.

Ditto to what Greg said. I would hang an 'unsafe' tag.

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

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.

Putting anti-sieze on the screws when you are installing them?

Down here in the swamp I will not use anything but stainless screws in any wet or damp location box. That steel strap can be a ball of rust but the screw will still come out. The slots are still good too.

This Corrosive Environment might warrant the use of Enclosures and / or Device Covers with NEMA 4X ratings.

Besides the Corrosion (Redox Reaction) Problems associated with the road Salts, the Material makes an efficient Conductive "Bridge", allowing "Semi-Impeded" flow of Charges (Electrons and Holes) via Na and Cl Elements.

Basically, the Arc Fault You + Your DVM's Leads experienced during the Voltage Test, may have been exacerbated (or fully due to) the Road Salts concentrations within &/or surrounding the Device (Receptacle).

Nevertheless, the Receptacle in the posted Image is beyond trashed; the Box is filling with Washed-Down Road Salt, and it looks like any attempt to backout the 6-32 Mounting Screws is hopeless at best!
(exception: large chisel to remove the screw heads...).

The "odd readouts" of the Plug-In Tester's Indicator Lamps, when reading these particular Receptacles, is likely due to the damage inflicted by the Rain Water + NaCl being splashed on them.
Notice the Corroded Brass of the Grounded Conductor's Terminal, on the "Lower" portion of the Receptacle.
The Brighter the Green Corrosion is, the fresher the Corrosion, which reduces the overall Conductive areas + increases Contact Resistance.

This could very easily cause the Indicator Lamps (Neon Lamps) to behave oddly.

If Salt concentrations build up within the Receptacle Device, inserting the DVM's Test Leads may have dislodged a chunk of NaCl, which fell across the tips of the Test Leads - resulting in an Arcing Fault.
Since this Fault is not a "Solid" Connection, the Fault Current Level would not fall within the OCPD's Trip Characteristics, and most likely drew no more than 40 Amps for <0.250 Seconds.
This is why you saw lots of Sparks and Arcs, yet there was no tripping of the OCPD.

If the OCPD for the Branch Circuit and the Panelboard's Main have the same Time-Trip Current Characteristics, a Solid Ground Fault will almost always (99.99999555% of the time) trip only the Main Circuit Breaker for the Panelboard, leaving the individual Branch Circuit OCPD closed.
If they both trip, it is because the same Load Current levels are flowing through both Devices at the same time.

Since a Panelboard's Main Breaker will typically have Currents from other Branch Circuits flowing through it, when a Fault occurs on a Branch Circuit, the Main OCPD has the highest Current Level flowing through it, and therefore falls into the Trip Range the fastest.


< end of TCC 101 >

Good luck with this Project.

--Scott (EE)

Probably not an option, but maybe the outlets should be mounted higher up in the wall, to avoid the salt getting up that high?

I would go back with a plastic FS box too.

Scott, thank-you for the info, that was an interesting read. Moving the receptacles to a higher elevation is not an option for likely 90% or more. Most are mounted on a concrete wall not much higher than 36" (this applies to the interior walls as well). Obviously there are concrete pillars but the distances in between would be impractical. IMO an easy solution to help increase the life of the receptacles would've been to use self closing weatherproof covers (the type that snap shut when when you release the cover). As I was testing the receptacles almost every cover was open to the elements. Nobody is closing the covers after they remove their block heater plug ends. The top level receptacles which are exposed to the sun look "baked" and are likely brittle.

If it were up to me I'd revamp the whole works but instead I have been instructed to fix the non-working/damaged receptacles only. It will forever be a high maintenance area until too much breaks down all at once.

Potseal, how many of the cover flaps on the receptacles have you seen broken off?

Here in Manitoba I have seen enough that I wonder why we just don't install standard interior wall plates. I don't know if its the -40 in the winter or the scorching sun in the summer that takes a toll on them.

Surprisingly most of the Eagle brand weatherproof covers are in good shape with only a few that I found damaged. Generally the receptacles that need replacing are far more deteriorated than the covers with the exception being the 4 corner cover screws. Must be an inferior type than the counter sunk centre screw since it's always the 4 corner screws that look rusty and often break during removal. Since the majority of the cover "doors" were found in the open position I assume they are seldom touched and that probably helps keep them intact but does nothing to help preserve the receptacle.

Potsael:
As Greg mentioned above have you given any thought to replacement of the boxes, covers, and receptacles with plastic items??

Carlon and others mfg surface mount single and 2-gang boxes and matching WP covers in plastic. Here in the states we have receptacles that are rated "WR" which are supposed to be 'weather resistant' and are NEC required for exterior installations.

I would suggest using corrosion resistant receptacles as well, such as the Hubbell HBL52CM62I, which is both weather and corrosion resistant. Details here: http://www.hubbell-wiring.com/Press/PDFS/H5254.pdf

I mentioned earlier that if it were my call to make I'd upgrade the whole works but this job has been determined by the higher ups that I simply replace with the same as existing. I could probably come back every 3-4 years and replace approximately the same number of receptacles. So far I've replaced 24. I'll likely replace another 16 before I'm done.