DC

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DCFIT

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Do you use the same safety precautions when working on DC like you do with AC? I always treat everything like it's hot but this DC current has me lil nervous. I was in a hurry and was on a roof top. Went ahead and hooked my lines up in my J box. I didn't realize that the panels energized my wire so quickly, I cut into my one set of lines and put out a small arc. I'm new to Solar energy and would like done advice from some pros. Thanks
 

kwired

Electron manager
Location
NE Nebraska
Do you use the same safety precautions when working on DC like you do with AC? I always treat everything like it's hot but this DC current has me lil nervous. I was in a hurry and was on a roof top. Went ahead and hooked my lines up in my J box. I didn't realize that the panels energized my wire so quickly, I cut into my one set of lines and put out a small arc. I'm new to Solar energy and would like done advice from some pros. Thanks

There is a current thread that asks if AC or DC have same shock potential hazards - part of the key here is voltage level for both current types. Even with lower voltages the risk of shock may be lower, but if the system has sufficient power available there still are risks of burns or fire starting capabilities from overheating of components AC or DC. Take a typical car battery 12 VDC, touch both terminals and you feel nothing. But there is still enough energy stored to make a pretty good arc or make a pretty hot conductor if it is shorted between the two source terminals.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Do you use the same safety precautions when working on DC like you do with AC? I always treat everything like it's hot but this DC current has me lil nervous. I was in a hurry and was on a roof top. Went ahead and hooked my lines up in my J box. I didn't realize that the panels energized my wire so quickly, I cut into my one set of lines and put out a small arc. I'm new to Solar energy and would like done advice from some pros. Thanks
Most installers leave one of the home run conductors disconnected from each of the module strings until all the rest of the DC wiring work is completed. Any time there is light on the modules, the voltage is there on the conductors. You are lucky that you only got a "small" arc.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
From an old thread...My advice on how to do it.

Install whips outside of the junction box. Leave these unconnected while you install panels and plug [the panels] into home-runs out on the array. Then test voltages [at the whips] for ground fault indications, then plug all the home runs into the whips at the same time. (For extra safety, plug in the ungrounded conductors first.)

-Your array is 'floated' without having to open up the inverter or leave it open until after the panels are installed.
-The procedure incorporates the proper testing of each string, which you should be doing anyway. You test string voltage to make sure you don't have a broken circuit. Then you test both positive and negative to ground to make sure you don't have a ground fault. You cannot test at a combiner where all strings are already connected if you want to know which string is the source of a problem.
-It's nice to have the whips for servicing if you have to come back later and replace or modify a home run on the array.

Note that some of this stuff doesn't apply to ungrounded systems (transformerless inverters) that have become much more common. The basic idea still holds though.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
From an old thread...My advice on how to do it.



Note that some of this stuff doesn't apply to ungrounded systems (transformerless inverters) that have become much more common. The basic idea still holds though.

It pretty much boils down to "don't be fooling around with the bare ends of energized conductors". I concur.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Volt for volt, amp for amp DC is more dangerous then AC for one simple reason. DC makes your muscles contract, which in turn under the right conditions like your hand clamped around a conductor, you would not be able to let go.

Another aspect of DC that can get you in trouble is with say low voltage system that have batteries in the circuit like a telecom plant or large off-grid solar system. The low voltage may give you a false sense of security as not being dangerous with respect to electrical shock potential. It maybe low voltage but large batteries can supply many thousand of amps of fault current. Enough to vaporize a wrench in your hand, your wedding ring, or engulf you in an arc blast when working over the top of them and drop something on top of them. Batteries can also explode when faulted near the terminal post sending covering you in battery acid along with setting you on fire.

Moral of the story treat AC and DC with the same respect. Both can make your survivors equally rich.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Maybe Amp for Amp DC is more dangerous, but milliamp for milliamp AC is far more dangerous because it can stop your heart at low current levels that would not be fatal for DC.
 

Zee

Senior Member
Location
CA
1.
Never work with live wires:

FIRST - Run all dc wire in conduit, lay dc wire in rack, land it in terminals in boxes and inverters, and crimp + and - plugs onto pv wire.
THEN - mount and connect panels.
In other words: you should never even touch a live wire, insulated or not.

Think of it this way: plugging in a PV panel to wiring is throwing the switch ON.
Why would you switch a circuit on, before you finished the wiring?

Always install in this order: Rack, Boxes, Conduit - Wire - Panels

2.
Remove GFDI fuse.
IF GFDI fuse exists, remove it - as soon as you un-box the inverter - and replace only after all work complete.
(The fuse itself creates a path to ground for accidental short circuits thru your body.......which is dangerous for personnel installing.)
Even better: use DC ungrounded inverters. Achieves same thing.

3.
I wear "Gorilla" gloves throughout the day. See if you like. They are rubber, come in very good size for me, like it was poured on my hand, help in gripping panels and i find them thin enough and comfortable enough that i don't keep removing them. They are - however - certainly not "electrical safety gloves". Sure there are thicker, 100% safe gloves, but i won't be wearing those all day. These..... i put on at 8 am and take off when i get in the van.

4. Never be in a hurry.
 
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