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I was trying to install CT clamps on the service wires to my center fed main electrical panel. I used pliers and by mistake torn a bit the insulation on one conductor while the pliers were touching the ground bar. There was an arc flash that pushed me back. Luckily no injuries. Visually I don't see any damage on the panel or wires. There was a burn smell for a while though. The CT clamp I was trying to fit got discolored from the arc flash.

This happened 2 days ago. Since then I restored power without any issues but I've kept the load low, no AC, no cooktop, no oven, no dryer.

Here is a picture of the wires that come from the meter to the main electrical panel and the CT clamp I was trying to fit. What gauge are they? Up to how many amps? This photo is before the arc flash. After the arc flash I don't see any damage on them. Only the insulation of the bottom wire was slightly torn but I couldn't see the conductor to assess any damage.

service wires before arc

Below is a picture of what's left of the pliers. The nose that was touching the ground bar is missing and I cannot find its missing part. The other nose that touched the conductor melted. Given the damage on the pliers I worry about any damage on the wires that might have derated them.

enter image description here

Is the panel and wires safe? Should I replace the main 100A breaker that was next to the arc flash? If it matters the breaker was off so there should be no damage on the busbar. As I said visually I don't see any damage in the panel. I mostly worry about the wires that come from the meter. Should I replace them to be safe? Can they be replaced?

Should I hire a licensed electrician to assess any damage? Will they just do a visual inspection or can they do any tests? Do I need to ask my utility provider to temporarily disconnect the meter so that the electrician can safely inspect or test the wires?

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    Might as well go buy a lottery ticket. The rest of the pliers is dust and smoke following a bit of time spent as plasma. Those look like insulated bus bars, not "wires" given the blatantly rectangular cross section and the way they are bent. Is this a "Meter-Main" type panel?
    – Ecnerwal
    Commented Jun 5, 2023 at 0:16
  • @Ecnerwal yes this is a meter main type panel. Yes I guess they are bus bars, not wires. They are flat, wide and inflexible. Does that make them less likely to have incurred a damage?
    – user162793
    Commented Jun 5, 2023 at 0:27
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    Re, "I cannot find its missing part" It probably now exists as a thin film of grime on the walls, ceiling, floors, and everything else in the room. Probably got a bit in your lungs as well. Commented Jun 6, 2023 at 14:33

2 Answers 2

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Here is a picture of the wires that come from the meter to the main electrical panel and the CT clamp I was trying to fit.

CTs cannot go there.

Those type of all-in-one's give you no option to install CT clamps there. And those were not within a mile of fitting, and the fact that you thought otherwise is concerning. It's not an option here, and it was a mistake to try. As you now know, those bus bars are totally unprotected by any overcurrent device, and current is unlimited. Well, limited at 10,000 or 22,000 amps by transformer and supply wire impedance, depending on power company rules.

10kA is 1.2MW, or a whole windmill, or 1/1000 of a nuclear plant, or about 1/8 the energy from a GAU-8 gun on the A-10 Warthog.

There was a few hundred dollars of money savings in choosing an all-in-one over separate meter-main and panel... and it has benefits (fewer unsightly enclosures) but trade-offs too, including no main CTs. Your only options are

  • ask the power company to let you into the line side of the enclosure and clamp the top of the meter.
  • clamp some individual circuits. (Note that it is not required for them to each get a separate clamp, but you will need to understand phasing if you combine them).
  • replace the all-in-one with separates.

As for the wire damage, get an IR thermometer and max out every 240V load you have for 20 minutes. Watch the temperature rise on the two and compare.

If you clamp some circuits you must be very careful that their phasing matches. Then you have your EVSE prevent those circuits + EV from exceeding the apportion those circuits get in the Load Calculation.

What gauge are they?

They have no gauge. They are not wires. They are rigid bus bars of rectangular cross section.

Up to how many amps?

That is determined by UL and specified in the panel labeling.

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  • Panel is rated at 125A i.sstatic.net/UMrzi.jpg I maxed out every 240V load for 40 minutes. Max current draw was 80A based on the smart meter. Average ~70A. Both rigid bus bars I was trying to install the CT clamps were at the same temperature ~75 degrees Fahrenheit.
    – user162793
    Commented Jun 17, 2023 at 5:21
  • @user162793 I'd call that a pass :) Commented Jun 17, 2023 at 16:53
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It is impossible to tell from the pictures if an electronic system is not damaged.

It is possible to tell that it is damaged, but not all damage is visible.

That being said: This is what I think you should do.

  1. Be grateful that you are alive and not dead. It doesn't seem like you have realized this, but you almost died. You are lucky (because I don't think you did this intentionally) that your pliers have rubberized grips that are designed to keep you from dying in instances like this. If you had pliers with damaged/worn away rubber handles, you would be dead right now.

As a general rule of thumb, turn off the power before messing with it. A licensed technician would have turned off the power before trying to install CT clamps.

  1. Hire a certified electrician, explain the stupid thing you just did and have them do the work for you. As based on previous actions, I don't think you are the best choice to work on anything electrical that involves main's power... And to be honest, doing work on anything involving mains power should be done by a licensed technician. Your utility company will require it (at least all of the utility companies I know of require it), they don't want you to knock out your neighborhood power/ blow up the local transformer/die from an arc flash.
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    An explanation for the downvote would be appreciated... If it is because I said" Hire a certified electrician" because you just tried to mess with the wiring of a live system and almost met your maker...
    – Questor
    Commented Jun 5, 2023 at 20:27
  • "And to be honest, doing work on anything involving mains power should be done by a licensed technician." Are you Australian by any chance? Because in most countries limited mains electrical work (installing light switches, plug sockets, etc.) is allowed to be DIY, and honestly is reasonably safe if you isolate the power first (and even if you don't, though of course you should, you often still have RCD protection). Commented Jun 6, 2023 at 10:47
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    @Crazymoomin installing light switches, plug sockets etc... Is not "involving mains power" that is residential work and the circuits are generally protected by a 20 amp breaker which you can turn off from your breaker box. And even if you don't the arc flash will trip the breaker (most likely)... Mains power is when you are messing with things that connect your house to the power grid, and is something that doesn't have a switch that you can turn off... And it won't trip off until after some serious amps have fried you. TLDR; Mains power is the electrical grid, not your houses circuits
    – Questor
    Commented Jun 6, 2023 at 15:10
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    OK, that's perhaps a mismatch in terminology there. In the UK, "mains electricity" is generally considered anything that operates at household voltage (220-240V) and above, regardless of what side of the consumer unit it is on. What OP is doing is almost certainly illegal here anyway, since you would need a licensed electrician to work on the consumer unit (other than flipping the breakers on and off). Anything on the "other side" is owned by the local grid company anyway so not even your local sparky can touch those. Commented Jun 6, 2023 at 16:56
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    @user162793 "Do I need to ask my utility provider to temporarily disconnect the meter so that the electrician can safely inspect or test the wires?" That you didn't do this before working on your power line? And then ask if you need to turn off the power of a system that experienced a short because it was live when you worked on it. While it is inspected for damages that you are worried exist?... If you had learned a lesson from nearly dying, turning the power off before working on a system shouldn't be a question you need to ask.
    – Questor
    Commented Jun 20, 2023 at 18:00

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