Electrical Safety When Connecting Solar Panels

[ftrost]

I am trying to determine what electrical PPE is necessary for when plugging the MC4 connectors and tying the solar modules together. Depending on the open circuit voltage per module, it will most likely exceed the 50 volt thresh hold. I am of the opinion that voltage rated gloves and PPE should be worn since the sun cannot be in a LOTO condition. I just want to make sure that I am not over thinking this and doing something not necessary. Thanks

 

[ggunn]

I am trying to determine what electrical PPE is necessary for when plugging the MC4 connectors and tying the solar modules together. Depending on the open circuit voltage per module, it will most likely exceed the 50 volt thresh hold. I am of the opinion that voltage rated gloves and PPE should be worn since the sun cannot be in a LOTO condition. I just want to make sure that I am not over thinking this and doing something not necessary. Thanks

My completely arbitrary opinion is that PPE is not needed to string modules. The only way you can get shocked is if you are touching both the positive and negative conductors at the same time, as neither has a path to ground to complete a circuit. Also, the conductive parts of a MC4 connector are recessed and difficult to touch.

 

[jaggedben]

MC4s are not intended to be either connected or disconnected under load. If proper procedures are followed, that won't happen. This can be done for example with LOTO on disconnects that connect strings to inverters or to each other. For this reason I don't agree with the logic that 'the sun can't be LOTO'. The risk, if any, is going to be from other paralled circuits, or an AC disconnect that turns on the inverter. And LOTO procedure applies to all of that. Also FWIW when it comes to the singular act of making up MC4 connectors, that risk is mainly arc flash, not shock.

You could make an argument that all modules should be tested to eliminate ground faults before plugging them in, to ensure the circuit is 'not live'. Beyond that, I agree with ggunn, at least with respect to connecting the modules of an individual string.

 

[ftrost]

Thanks-I guess I need to restate my situation. There is a contractor in my area who wants to use several 1st year apprentices for a utility solar installation (500 acres). I am the training director and will not be on the job. I have concerns about the apprentices building a fire in their hands since voltage will be present and they might be put into a bad situation which I want to avoid. I am wanting to develop a plan since I have concerns that the contractor is way over their head and I want to make sure that someone doesn't end up in the burn unit. Thanks

 

[Birken Vogt]

It is my understanding that MC4 connectors were invented so that people could plug and unplug them energized without hazard. Much like an outlet on the wall.

My personal practice is to make sure any load control (breakers, loads etc.) are turned off/open, then plug away so no current is being made or broken, then plug away. The voltage is only potential and not really a hazard as the connections are all well shielded.

 

[jaggedben]

Thanks-I guess I need to restate my situation. There is a contractor in my area who wants to use several 1st year apprentices for a utility solar installation (500 acres). I am the training director and will not be on the job. I have concerns about the apprentices building a fire in their hands since voltage will be present and they might be put into a bad situation which I want to avoid. I am wanting to develop a plan since I have concerns that the contractor is way over their head and I want to make sure that someone doesn't end up in the burn unit. Thanks

I hear you. I'm not so concerned about them being 1-year apprentices but I'm concerned about how you describe the contractor.

No way I can lay out a whole plan for you here but if I were you I'd emphasize these three things in addition to PPE and whatever else.
First, drill into these apprentices that any given string of modules are only connected to each other, not to any home run wiring, until the proper time and procedure for connecting strings to combiners or whatever. (Good idea to tag out the ends of prepared strings and home runs when they're ready.)
Second, push the contractor hard to have a detailed, written, and organized procedure for connecting the strings in parallel at combiners or wherever. I think PPE for that part is totally appropriate. Not something the first years should be doing without supervision.
Third, make sure they include testing for polarity and ground faults on each string as part of the procedures.

An individual string is very unlikely to send someone to the burn unit, even if they forget to use PPE. The potential dangers involve lots of parallel strings being connected in a short circuit because something got reversed or faulted through being disorganized.

 

[ftrost]

Thanks-This was the type of stuff that I was thinking about. I wanted to make sure that I wasn't out of bounds. Thanks

 

[pv_n00b]

With a large ground mount system using central inverters the arc fault incident energy available at any particular MC4 could be high enough to be concerned about if all the parallel strings are connected through to the recombiner. In systems with string inverters, the incident energy is often less than 1.2cal/cm^2 and requires no PPE. I have clients who want me to bump up the incident energy on the AF labels just to get workers to wear the minimum level of PPE required at 1.2cal.
I was at a site where an electrician opened up the supply side of a good-sized service SWBD wearing no PPE. They said during the inspection that they should close up the SWBD before a bird flew in and caused an AF. This is either just a case of "I don't need no stinking PPE" or an acceptance that no PPE will protect someone when opening the utility side of a service SWBD so why be uncomfortable when you die?

 

[ggunn]

With a large ground mount system using central inverters the arc fault incident energy available at any particular MC4 could be high enough to be concerned about if all the parallel strings are connected through to the recombiner.

I'm not sure what you mean. The available current at any MC4 connection is only that of a single string, which is the Isc of a single module. Certainly within a big DC combiner there is lots of DC current available at the busbars, but not on individual string wiring outside the combiner.

 

[jaggedben]

I'm not sure what you mean. The available current at any MC4 connection is only that of a single string, which is the Isc of a single module.... ..

You're assuming everything is wired properly and no one makes a mistake, which is precisely what cannot be assumed and requires procedures and methods to assure. Otherwise your statement is false.

Let's take an example mistake that I've seen happen for real, thankfully on a string inverter system not utility scale. Positive and negative jumpers for a string were brought to a single location, along with the home run plugs. Two positive and two negative MC4 connectors in one location. When it was time to plug them in, installer got confused and plugged the jumpers to each other, shorting the string. He also plugged the home runs to each other, shorting the other string in the system (via the parallel connections at the inverter). If this had been a utility scale system, then he would have had the full fault current of however many strings were already paralleled at the inverter when connecting two MC4s together.

(One lesson here is to put enough distance between home run plugs to make this difficult.)

So don't make the assumption that plugging in MC4s inherently can't result in major arc flash. On a utility scale system, people in charge have to take measures to insure it can't happen.

 

[jaggedben]

Also the available fault current from a single string is certainly enough to burn your bare hands if you connect or disconnect them under load. How do you insure that the system isn't put under load and then someone finds a string that was never connected and plugs in the MC4s? Again, procedures.

 

[pv_n00b]

I'm not sure what you mean. The available current at any MC4 connection is only that of a single string, which is the Isc of a single module. Certainly within a big DC combiner there is lots of DC current available at the busbars, but not on individual string wiring outside the combiner.

If everything is connected then the available fault current at any given MC4 is from that string and every other string that is in parallel with it.

 

[ggunn]

If everything is connected then the available fault current at any given MC4 is from that string and every other string that is in parallel with it.

But that fault current is not available to a ground fault.

 

[pv_n00b]

But that fault current is not available to a ground fault

I'm not limiting this to ground faults.

 

[JimInPB]

I usually throw a towel over the panel before messing with the wiring. A little bit of sun still gets in & a little voltage gets generated, but not much.

 

[jaggedben]

I usually throw a towel over the panel before messing with the wiring. A little bit of sun still gets in & a little voltage gets generated, but not much.

Not easily done over 500 acres. (See post #4.)