Live upgrade from old to new combiner

Riley

Hi, I’m in the process of upgrading my roof top PV array from 12 panels to 18 panels (4 strings to 6 strings). Note that these are roof top mounted and I’m not doing ground mounting for a number of reasons (plus the panels are now mounted). In order to do this, I am changing out the 4 string combiner to a 6 string combiner. Also note that most of the MC-4 connectors of the original 12 panel array are mounted under the array and are not accessible.

So I’m looking for safety advice/tips to do the moving of the live PV wiring from the old combiner to the new combiner. I’m well aware that the load (current flow) needs to be disconnected before opening any connections. Once that load is removed, I plan to move the strings one by one from the old combiner to the new combiner. Each string will have approximately 120vdc with a max current of 10 amps. The max current would be much less as I plan to do this combiner swap in the 3 or 4 hours of morning time when the panels are heavily shaded and should have a max current of about 1 -> 3 amps.

I am thinking I should wear electrical insulating gloves but thin enough that I can actually work effectively. I will be careful as possible but looking for other tips AND advice on good gloves. Given both neg and pos are floating with respect to ground should help things a bit but I know I shouldn’t rely on this.

Please don’t tell me to do a ground mount as that’s not in the cards (my roof top is the only good sun exposure) and don’t tell me to disconnect the MC-4 connectors, as I said, many are inaccessible.

Thanks in advance.

BB.

Are you only working with MC4 connectors, or are you going to be cutting/splicing/crimping?

The MC4 connectors are reasonably shielded and should be OK to disconnect/connect while "live". Note that you do not want current flow/loads while making/breaking connectors--The arcs created while servicing the connectors under current/load can damage/ruin the contacts.

An example of insulated lineman's gloves:

https://amazon.com/electrician-gloves-insulated/s?k=electrician+gloves+insulated

A friend of mine had a "real set" of lineman's gloves--They both had the (relatively) heavy rubber gloves, but also a nice set of leather gloves worn over the rubber gloves to prevent cuts and punctures while working on the live cables.

As always, it is difficult to "teach" save practices for working with line voltages on a forum... Having additional safety is also a good idea (harness to catch you if you fall, working with a second person to ensure all goes well, etc.).

-Bill

DanS26

Break each string MC-4 connector the last one on both the positive side and negative side before the combiner box.  That will allow you to work in the combiner box without any possibility of current flow or accidental shorting.  After you have the combiner box completely wired, then go back and reconnect the final MC-4 connector in each string positive and negative.  Also make sure no inverter load is being required.