Risk when connecting/disconnecting solar panels in the sun??

Susido · March 2016

I know I've generally worked on my solar panels during the daylight because being able to see what I'm doing really helps. But I've read a few references recently about how bad a practice that might be. Like this one from another forum in reference to using coax cable connectors:

Warning, just like the MC-4 or other Solar panel connectors,
these can NEVER be unplugged or plugged in while the sun is on the panels..
The power will arc weld/melt the center pin. It will have to be replaced.

I've done a lot connecting and disconnecting MC-4 panels under often bright sunlight and I've never noticed any problems though this has been with low-voltage 12v nominal panels. Do most people work on their panels at night or first cover them with blankets or what?

Vic · March 2016

Susido,

First, one should only work on PV cabling with all of the Protective devices in the OFF, or open position -- usually these will be circuit breakers. This means that there should be zero current flowing in these cables, and therefore should not be able to arc.

It is by far safest to work on PV systems with the PVs covered, but, with larger arrays, it can be difficult to cover all of them. One can sequentially cover the PV string that is being worked on.

One can pull all the cables for the PV strings, and make all Combiner connections before ANY PV cables are connected. With all of the Combiner breakers open, one can cover a single string of PVs, and connect all of the MC connectors on only that string, move the cover to the next string ... and so on.

Higher DC voltages have greater arc "potential" than do lower voltages. DC voltages are much more LETHAL than are AC voltages. A surprisingly small current that flows through one's chest can stop the heart. And, DC voltages often cause muscle contraction, which can make the connection to the human lower impedance, which can cause more current to flow.

Even a non-lethal DC shock can result in injury, as one tries to extract him/herself from the potential.

High voltage systems require extreme care when working on any part of them.

FWIW, Vic

Photowhit · March 2016

I wouldn't and don't know of any installer who covers panels. Just turn the breakers off and do your work, not breakers, no circuit, no current.

I wouldn't worry about low voltage and MC4 connectors. I've seen people fret, but if you did a couple/few connections while a 12-24volt system was hot, I think you're fine, They are designed to have many contact point (Multi-contact connectors) The current would flow through the first 100 points and as you insert the connector it would wipe/expose oxidized metal. MC3 and MC4 connectors make contact well away from exposed skin so shock hazard is pretty much non-existent and 12 and 24 volt have much less arc potential.

Long strings with high DC voltage would be another story and I don't want to minimize their potential to arc!

Dave Angelini · March 2016

High voltage strings can easily kill you! Definitely wait until evening/early morning or cover the array and shut down input/output breakers.

Xizang · March 2016

WHAT would you guys consider safe volatages vs. dangerous voltages? Apparently we all agree 12 VDC is relatively safe (unless you get your wedding ring across the wrong contacts). How about 24 volts DC? And does available amperage behind those low voltages affect safety in touching or handling (other than unexpected arc welding).

zoneblue · March 2016

Id be cautious on anything above a single 36cell panel.

https://www.youtube.com/watch?v=trmxzUVT2eE

Xizang · March 2016

zoneblue said:

Id be cautious on anything above a single 36cell panel.

https://www.youtube.com/watch?v=trmxzUVT2eE

And typically, that 36-cell panel produces about 20 to 21 volts? Or is that 1 volt per cell = 36 volts?

vtmaps · March 2016

Xizang said:

And typically, that 36-cell panel produces about 20 to 21 volts? Or is that 1 volt per cell = 36 volts?

Vmp is typically about 1/2 volt per cell. Voc is about 20% higher. Thus 36 cell panel has Vmp about 18 volts and Voc about 22 volts.

--vtMaps

Photowhit · March 2016

Respect any circuit, much of this can be done by NOT making a circuit!

I would doubt you could get a 100 volt string of DC to arc out of a MC4 connector even if one side was unprotected! but there is no reason to work on a live circuit. Shut it down at the fuse or breaker, do your wiring and the complete the circuit by closing the breaker or installing the fuse. You can wait until morning to make the finial connection if desired, I would not install a fuse under load!

I don't like the video, since it implies that AC is safer than DC to work with, it's not.

bill von novak · March 2016

Photowhit said:

Respect any circuit, much of this can be done by NOT making a circuit!
I would doubt you could get a 100 volt string of DC to arc out of a MC4 connector even if one side was unprotected!
I don't like the video, since it implies that AC is safer than DC to work with, it's not.

You can definitely get an arc (a quite impressive one) with 100 volts DC. I found this out one day when I tried to connect a string of four panels (about 80 volts) while it was live. The arc was about half an inch long and maintained itself pretty well.

AC is generally safer to work with than a similar DC voltage, for several reasons. Doesn't mean you can't work with DC safely, it just means you have to be careful.

Xizang · March 2016

I've always thought of powerful electric circuits being the same as my guns. Handled carefully, responsibly, conservatively and with respect, they are both very useful tools. But recklessly, either can be immediate death.

zoneblue · March 2016

PW, true, while AC "hurts" at a lower voltage because more current does flow with AC because of the non resistive components to the bodies impedence. However AC does provide the body short regular intervals in which to maybe relax the muscles long enough to release your grip. Logically that only applies where you have your hands wrapped around both conductors, or a similar situation where your muscles contract preventing you from releasing.

Old time sparkys have a rule when working near live circuits, always have one hand behind your back. For my part, ive a had a belt off 230V, (when i was young and stupid), and the open hand contact contracted the muscles in my body to such an extent that i was thrown backwards and hit my head on the wall, which probably hurt more than the burnng ache in my hand.

Vic · March 2016

Photowhit said:

Respect any circuit, much of this can be done by NOT making a circuit!
I would doubt you could get a 100 volt string of DC to arc out of a MC4 connector even if one side was unprotected! but there is no reason to work on a live circuit. Shut it down at the fuse or breaker, do your wiring and the complete the circuit by closing the breaker or installing the fuse. You can wait until morning to make the finial connection if desired, I would not install a fuse under load!
I don't like the video, since it implies that AC is safer than DC to work with, it's not.

Hi ..whit,

Not to be too argumentative, but, IMO DC voltages can be considerably more dangerous than the same AC voltage would be, for humans. Primarily due to the fact that a sufficiently high DC voltage can/will cause muscle contraction, which makes it more difficult for the human to release from the source of the potential. In days long-past, it used to be said that about the most risky DC voltage was about 450 volts. It was said that this potential could cause strong muscle contraction, without causing a lot of skin burning that would be associated with higher DC voltages -- this is something that I have never tested (thank goodness).

AC voltages, due to current reversal at the frequency of the potential do not have this contraction "feature".

More recently, however, it seems that there have been cautions to seek medical review of subjects that have been shocked, even by AC voltages -- this might just be a Liability-limiting desire on the part of companies. But, it has also been stated that there can be additional negative effects of AC shocks on those of advanced age ... Dunno, just do not like to be shocked at all.

Also, some of the comments advising caution stem from the desire to not dismiss the possible risks, on a general info Forum, such as this. One cannot assume that everyone reading these posts have sufficient experience and knowledge to always do things to reduce the personal risk on working on electrical systems ... and so on.

FWIW, Vic

BB. · March 2016

In general, these days (last few decades) have been much more careful about electric shock.

Old days--Still breathing after a shock--Go back to work.

Recent times--Shocked by 120 VAC, doctor visit, time off.
Recent times--Shocked by 240+ VAC, overnight in hospital regardless of how patient feels.

There have been enough instances of folks dying hours after a good jolt, that businesses (Cal OSHA, etc.?) do not take anything for-granted.

To the point, where a company would specifically hire a licensed electrician to work on "hot circuits" in the old days--To all circuits are shut down and locked before service.

What is a "dangerous voltage"? 12 volts or less is usually safe (should be current limited to a few amps or less).

Nice paper on question (from a UL/NRTL point of view):

http://www.staveb.ch/downloads/1692-wp001_-en-p.pdf

0.2.1 Electric shock
Steady state voltages up to 42.4 V peak, or 60 VDC are not generally regarded as hazardous under dry conditions for an area of contact equivalent to a human hand. Bare parts that have to be touched or handled in the normal course of events should be at earth potential or properly insulated.

With sweaty hands, sitting on metal--You can feel a 24 volt shock. Secondary efficect should also be thought about... Standing on a ladder, working over dangerous mechanical/electrical systems, etc.--And what happens if you are shocked (fall in, drop tools into work area, fall from ladder, etc.).

-Bill

Photowhit · March 2016

Vic, Not sure when I ever said DC wasn't dangerous? NEVER DID!

I did say I didn't think you could get it to arc out side of an MC4 connector. If someone sustained a 1/2 inch arc, I actually think it would be within an MC4 connector, There is a good bit of distance there.

And to whom ever had an arc from a 100volt DC, YOU HAVE NO NEED TO BE ANYWHERE NEAR MY ARRAY! You should have other people doing your work!

I don't yell often, but DO NOT MAKE A CURCUIT! You can do all your installation with out making a circuit. Then complete the circuit by closing the breaker.

Be safe!

Vic said:

Photowhit said:

Respect any circuit, much of this can be done by NOT making a circuit!
I would doubt you could get a 100 volt string of DC to arc out of a MC4 connector even if one side was unprotected! but there is no reason to work on a live circuit. Shut it down at the fuse or breaker, do your wiring and the complete the circuit by closing the breaker or installing the fuse. You can wait until morning to make the finial connection if desired, I would not install a fuse under load!
I don't like the video, since it implies that AC is safer than DC to work with, it's not.

Hi ..whit,
Not to be too argumentative, but, IMO DC voltages can be considerably more dangerous than the same AC voltage would be, for humans. Primarily due to the fact that a sufficiently high DC voltage can/will cause muscle contraction, which makes it more difficult for the human to release from the source of the potential.

zoneblue · March 2016

As PW said the simple solution is to wire the array with the PV breaker off. You can hot plug a mc4 in daylight just fine so long as you keep your pinky fingers tucked clear, and the circuit is not live. Just be mindful of what you are dealing with. The common 2S 60 cell, and 2S 72 cell arrays are fine with this approach. If i was wiring a 600V array, then id be lots more careful, in fact id get some other sucker to do it.

Xizang · March 2016

NOW you guys have me scared of my 24 volt system!

Photowhit · March 2016

Xizang said:

NOW you guys have me scared of my 24 volt system!

If you want to feel a little more comfortable, The NEC code requires voltages ABOVE 30 volts to have limited access. While 24 volt systems will run above 30 volts. NEC tends to be cautious.

scrubjaysnest · March 2016

Seems I saw some where the general rule is fuse or breaker for every two panels. When I worked at the power plant our back up was 125vdc battery bank feeding 25kw inverters. Always had two people when working on the battery bank. One was the safety man. The sparkys were more unnerved working the 125 vdc then the 4160 vac stuff.

bill von novak · March 2016

scrubjaysnest said:

Seems I saw some where the general rule is fuse or breaker for every two panels.

The general rule is fuse or breaker for EVERY string if you have more than two strings. That means you could have a 24 panel array with no fuses, or a three panel array with fuses. It all depends on how it is set up.

nsaspook · March 2016

Generally DC voltages pose a much greater arc danger above about 24 volts.
Once you get past 100 volts DC the arc power is usually enough to sustain a destructive arc easily.
https://youtu.be/Zez2r1RPpWY

Xizang · March 2016

Yet 24 and even 48 volts DC have been common for years in electrical systems in heavy equipment, military equipment, boats and ships, trains, mining equipment, etc.

What's the voltage in standard arc welders?

BB. · March 2016

I guess if you believe a random Wiki entry, somewhere between 17 to 45 volts for a typical (smaller generic) arc welder.

Remember though, arc welders are (usually) constant current devices (you set 50 amps, and the transformer/ballast will limit current to maximum of 50 amp regardless of the voltage).

And the actual working voltage at any time is related to the length of the arc. Short arc, lower voltage--Long arc, higher voltage.

-Bill

kaipo_boy · April 2016

When I'm welding TIG in ferrous metals (I'm holding the negative electrode in my hands and the workpiece I'm welding is positively grounded) the readout on the machine is usually in the 20's (volts). As BB said, it varies with how far you hold the electrode from the workpiece. We hold as close as we can without actually touching in order to obtain the cleanest weld with the most heat directed into as small a spot as possible to prevent distortion and annealing effects in the nearby metal. Usually this is in constant current mode at around 50 amps for most of my work (very small precise welding for tooling or gunsmithing). The arc length would be around 1mm but if I draw away from the work after establishing an arc, it can draw out to an inch or more before snapping off. Interestingly, if you reverse the electrodes the heat moves with it. With the above setup the majority of the heat is in the workpiece; if you reverse it, the majority of the heat goes into melting your electrode and usually that process is with automatic wirefeed called MIG.

Personally, I just waited until dusk when connecting my 3 panels (280w each) up... since it was a cobbled together temporary system only. I am now adding a combiner box with breakers to that system to make it more permanent.... although, with lead acid batteries slated to last only a few years, one might reasonably call all lead acid systems semi 'temporary'

LeNerd · July 2016

Hi new here and to solar and electric even kinda.
In short, is the reason for not working with high voltage in the sun even with everything open That there may be a short some where and there for Arcing may occur even though one may think it is impossible?
I have a 600volt ground mount system 36-250w modules in 3 strings going to an SMA inverter at the home. I was dumb enough to put it together myself. I have everything wired together (Junction Box at the array, DC disconnect, inverter, AC disconnect and revenue grade meter) The idea was to do the scary stuff tomorrow. PV modules to themselves and strings to the junction box connecting my DC to the 150ft run to the SMA converter and then to put the breaker into my service box. I wanted to get the MC4s onto the extension wires before dark and then plug in at night. Am I right to think that it is safe to string up the modules in the morning light but shouldn't connect them to the rest of the system unless they are covered? even with the DC disconnect and AC open?

Vic · July 2016

Hi LeNerd, Welcome to the Forum,

The largest RISK is from ELECTROCTION. Arcs at these high voltages are dangerous, and can be damaging, as they are difficult to extinguish.

Why not string the PV up at night with a good LED work light, it is a ground mount, so there should be no risk of falling off a roof ...

Cautious Vic

BB. · July 2016

If you have never worked on "hot circuits" before--This is not a great place/time to learn. In general, making sure switches/breakers/fuse panels are "open" (disconnected)--You will not get any arcs/sparks (or very small ones).

Using insulated tools (plastic handles, wrapping NEW electrician's tape around pliers/cutter handles/around wrench handles) makes things safer. Working with "one hand" and no jewelry (rings, chains).

There are two major dangers. One is Arcs--Can start fire. And a spark you did not expect cause you to jump (fall of ladder, grab a "hot wire", etc.).

The second major danger is electrocution... It does not take much to stop your heart (0.010 amps or 10 milliamps is enough). It is not the voltage--It is the current passing through your chest cavity. Above ~40 volts you run an electrocution risk (sweaty hands, wet clothes, etc. make things worse).

Solar panels make voltage with very little light--Weak morning sun is more than enough light to run the panels up to rated voltage (Voc). There will not be much current in weak light, but more than enough to kill you.

Getting hit with 120 VAC is enough to get you into a hospital, and 240 VAC hit will get you checked in overnight--Even if you feel fine (Cal OSHA workplace rules as I understand). This is from direct workplace experience with electricians getting "minor" shocks at work and dying up to 24 hours later with no obvious symptoms.

If you are careful and respect the voltages present--You can do the wiring connections hot--But you may not know you are doing something wrong until you get bit. And making connections to equipment "hot" can give you good sized arcs/sparks even if off (charging input capacitors for inverters is a common cause). Just beware that this is common and don't let it surprise you (fall from ladder, drag hot wire across connection panel, etc.).

-Bill

Photowhit · July 2016

Work 1 handed and rubber soled shoes!

Ethan Brush · July 2016

Susido said:

I know I've generally worked on my solar panels during the daylight because being able to see what I'm doing really helps. But I've read a few references recently about how bad a practice that might be. Like this one from another forum in reference to using coax cable connectors:

Warning, just like the MC-4 or other Solar panel connectors,
these can NEVER be unplugged or plugged in while the sun is on the panels..
The power will arc weld/melt the center pin. It will have to be replaced.

I've done a lot connecting and disconnecting MC-4 panels under often bright sunlight and I've never noticed any problems though this has been with low-voltage 12v nominal panels. Do most people work on their panels at night or first cover them with blankets or what?

I have a done a bunch of 300KW to 1 meg 1000V systems and no we dont cover panels or work at night. Wearing gloves wouldnt hurt, but I dont even feel the need to do that clipping MC4's together. Note MC4's are ok to connect and disconnect "live" but not under load. Just keep your sting fuses out until everything is clipped.

Dave Angelini · July 2016

Right and soon there will be 1500 vdc systems and safety can't really be minimized at this level.
Most here have never done any of what you are talking about and the way people read this when they do not have training can be dangerous.
Some do not have string fuses and so even more chance to be the guy laying on the ground in all those warning pictures.

WaterWheel · July 2016

A while back I was replacing a non working charge controller that had been hooked to over 280v shortly before. I had disconnected all wiring and pulled it out of the box and was using a screw gun to pull the controller off the wall. My forearm touched the bare metal on the edge of the controller while my other hand was holding the controller. Got a nasty shock, felt like an electric fence for one short pop.

I'm still not sure what happened. I had disconnected all power at the breakers before unhooking the wiring. There must have still been some power in a capacitor in the controller. Either way when ever I'm dealing with a faulty device in the future I think I'll keep an earth ground on it for a while even if it's only a temporary jumper.

Risk when connecting/disconnecting solar panels in the sun??

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