Is there any danger in plugging in MC cables?

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Is there any danger in plugging in MC cables?

Postby stevetull on Tue Dec 12, 2017 7:27 pm

Does anyone else wait until nightfall to make the final connections of solar panel strings to combiner box? Or am i just being a wuss?
Breakers in combiner box will be off.

Thank you.

-Steve
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Re: Is there any danger in plugging in MC cables?

Postby sodamo on Tue Dec 12, 2017 8:01 pm

Never really thought about it. Have always hooked mine in during the day.

How many installers do you know that come back after dark to connect?
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Re: Is there any danger in plugging in MC cables?

Postby blackswan555 on Wed Dec 13, 2017 12:33 am

Not night but I always leave one panel per series string disconnected whilst I have my hands "in there", You can still sometimes get a little tingle, But compared to a possible 120v plus DC tingle, it is nothing (120v DC will kill you on a bad day)

Tim
My comments are based on my experience and research, They are not endorsed or checked by Outback.I am an independent British electrician living in Spain, So please take this into account when reading /acting on my post`s.
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Re: Is there any danger in plugging in MC cables?

Postby JRHill on Wed Dec 13, 2017 1:18 pm

blackswan555 wrote:120v DC will kill you on a bad day
.

This is for real, make no mistake. I've had high voltage mishaps with AC over the years but never DC. So I can't say from experience except that AC will throw you and it has been said that DC will make you hold on.

Personal memory: I was a journeyman machinist apprentice. On a locked out unit, the the master plant electrician said "Hey, kid, com'ere and look at this." With a bunch of on-lookers, he put his hand around my shoulders and with a fast sweep went across one lug of a 440vac 3ph connection. It didn't affect him. It threw me a ways away to the floor. OSHA would've had a heyday but I'm sure there wouldn't have been any witnesses. But the lesson had it's intended affect: Never, never be a path to ground. Not much later I learned to never make connections, on or off and under load, if there is any way possible to avoid doing so. Some memories never fade.

Best,
Jim
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Re: Is there any danger in plugging in MC cables?

Postby Mike Curran on Wed Dec 13, 2017 1:42 pm

When I adjust the tilt angle on my upper array, I routinely unplug the MC connectors in the daytime to allow each section of panels to be moved separate from the adjacent, as-yet-unmoved section. I always open the PV breakers first - if you unplug them under load you'll see one heck of an arc that won't self extinguish like an AC current arc does. And you're putting yourself in harms way.

With the PV breaker open the only danger is if you somehow put yourself between the positive and negative leads of one, two or more panels in series, where you'd be exposed to anywhere from 40 to 80 volts DC, or more. Not a good place to be, but you'd almost have to be trying to do this on purpose for it to happen. Still, discretion is the better part of valor.
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Re: Is there any danger in plugging in MC cables?

Postby JRHill on Wed Dec 13, 2017 1:46 pm

Mike Curran wrote:Not a good place to be


Well said. But, Mr. Mike, you don't have a steel roof ;-)

Speaking of which, I tied my roof to the system ground with heavy copper many years ago. No, no lightening rods as it's very rare for lightning hits in this area (mostly dry lightning with no or little noise but lots of forest fires). But what have others done for protection along these lines? I know that one conductor is a joke - if serious I'd have at least two or four.... Is this a multiple ground fault if, in my case, it were to be expanded?
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Re: Is there any danger in plugging in MC cables?

Postby Mike Curran on Wed Dec 13, 2017 2:10 pm

JRHill wrote:
Mike Curran wrote:Not a good place to be


Well said. But, Mr. Mike, you don't have a steel roof ;-)

Speaking of which, I tied my roof to the system ground with heavy copper many years ago. No, no lightening rods as it's very rare for lightning hits in this area (mostly dry lightning with no or little noise but lots of forest fires). But what have others done for protection along these lines? I know that one conductor is a joke - if serious I'd have at least two or four.... Is this a multiple ground fault if, in my case, it were to be expanded?


I have a steel roof on my barn where my Westinghouse Solar array is mounted. The only ground I have is for the panels themselves, which are in turn framelessly bolted to the standing seam roof with S5! mounting blocks and L brackets. The S5!'s are clamped pretty tightly to the standing seams but I don't think it's a good electrical connection since the metal is painted. No lightning rods on mine.

Googled lightning rod steel roof and got this (link), which says in part "Steel roofing materials are no more attractive to lightning than any other type of roofing material, according to the Metal Roofing Wholesalers website." Of course what do I expect from a roofing rep? :smile:

https://www.hunker.com/13417835/does-a- ... d-attached
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- 2 grid-tied GVFX3524's classic stacked for 120/240VAC
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- Hub10.3, Mate3, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

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Re: Is there any danger in plugging in MC cables?

Postby JRHill on Wed Dec 13, 2017 2:51 pm

Always trust the sales guy and to the trade folks, always trust the guy with seniority. To me, both folks are similarly (un)believable unless you suspect otherwise.

(not to dis the trades but it is a long standing game in both professions). Sincerely, for the hope of all of us - I hope more young will enter the trades. We need many more skilled trade"folks" entering. Without "Perfect" "Like...." "Awesome" and one can follow a technical conversation.

I have eleven in this age group with profoundly mixed results. It always seems to hinge on "Friends" and I hope it's not the TV show.
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Re: Is there any danger in plugging in MC cables?

Postby sodamo on Wed Dec 13, 2017 9:38 pm

Upon reflection, maybe a bit more detail.

When working in my Combiner boxes, breakers are off unless checking with multimeter.
If working a particular set of panels, breaker off and the closet mc4 open if making the combiner connection, then I reconnect then throw the breaker and test.

I have a steel roof. I run a bare copper conductor to each panel then combine then to grounding point. Also lightning arrestees at the Combiner and the Outback DC side.

I had an AC learning experience when younger, maybe Soph/Jr in HS. My Dad was an Electrical contractor, so my brothers and I were the helpers. One summer he had a project at the local elementary school, Don’t remember what. He had me wrenching some connections in one of the disconnects. Actually, the only detail I remember is hitting something with that wrench and it getting flung across the room. Then I was admonished for not paying attention. He told my Mom when we got home so I guess I wasn’t in danger, but it sure got my attention and 50+ years later it is the one thing I think about whenever I’m working in an electric box - before and after I make sure it is off.
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RTS
4 FM 80 charge controllers
FNDC w/3 shunts
Mate 3
OpticsRE - Piha Kahuku
21 Aquion Aspen 48S (46.2 kw)
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