Curious why this would happen and if there was ever a danger. 20 laptops hooked up to two powerstrips (I don’t think surge protected) @ 10 each strip. Those go into a third powerstrip but the ground prong for the two strips (i.e. the ones the laptops are plugged into) have broken off. The third strip has the ground prong and as I was plugging it into the outlet, there was a spark on the ground plug to the ground hole of the outlet. I don’t think there was a connection make yet on the hot & neutral prongs. I’ve seen sparks on the hot line but why would there be a spark on the ground prong under those circumstances? I know that it was probably similar to rubbing feet on the carpet and grounding yourself by touching a doorknob but given the prongs were not touching any metal and there should not have been any static buildup on that wire I am at a loss as to where the charge came from.
Unbalanced load, perhaps?
It could be static electricity discharging through the ground connection. If so then your equipment is retaining this charge with the prongs broken off. I believe this is called a “floating chassis ground”, and generally that’s a bad thing. Considering the price of 20 laptops, I’d suggest new power strips and a surge protector. Better safe than sorry.
Is this a workplace, there may be laws requiring all the ground connections be in place. Is there an insurance policy, any claim might be denied.
Is that the same thing as when guitars and microphones have an improper ground and they end up shocking or electrocuting someone? Could that have happened from the laptop side because the main strip hadn’t been plugged in.
The answer to the second question is no, the chassis ground of the laptops and two power strips are isolated from the third power strip, which in turn was isolated from Earth ground. I’m assuming the ground circuitry in the third strip picked up a little charge and this quickly discharged to the Earth ground as soon as you made that connection. The laptops and two power strips are still isolated from Earth ground.
The advise to replace the power strips and add a surge protector eliminates any internal issues that might cause this, they need replaced anyway …
The answer to your first is a qualified yes, it could be a floating ground but I’ve heard tales of musicians getting WHALLOPED by 110 VAC on stage … making guitar solos tougher as it were.
Are you plugging in power strips into other power strips? And some power strips with broken grounds?
If this is in a work environment you are in violation of fire code and OSHA.
When I worked in a hotel Banquets would often try this multiple set up and then complain when the breaker tripped. I would not reset the breaker until they eliminated the multiple connections.
The OP’s setup is a bit dangerous.
Power strips often have “surge protectors” in them, which I put in quotes because the cheaper ones will just shove an MOV in there between hot and ground and they’ll call that little thing a surge protector (not exactly the greatest surge protector in the world…). Without the ground terminal being actually grounded, this can cause the protective ground on the laptop side to float up to 120 VAC. Granted, the voltage is going across the MOV which will limit the current you get from it, but still, anything metal connected to the laptop chassis will have 120 VAC present on it. Most laptops don’t have much exposed metal, but there are bits like the shields around video and USB ports and screws for disk drive covers and the like.
Replace the power strip with the busted ground ASAP.
I can’t see this problem causing the spark that the OP describes though, as the hot and neutral weren’t even connected yet and therefore you shouldn’t have had any voltage anywhere on the laptop side of the plug. Maybe it was a static discharge.
As for musical instruments, the strings on an electric guitar or bass and the outside of a microphone are all electrically connected to the instrument’s ground, which connects to earth ground at the amplifier. If the earth ground floats, all of those can become shock hazards. Many people have had the bejezus shocked out of them by an ungrounded amplifier, and a few have even been killed from it.
Deaths from guitar amps were mostly in the days of floating chassis. The trick to reduce induced noise was to connect the metal chassis to the neutral with a capacitor. In principle this would provide a low impedance path for audio frequencies, and thus effect a grounded system well enough to avoid noise. The downside was that you had a significant chance of someone reversing the active and neutral in the chain between the amp and the real active and grounded neutral. Bad socket wiring, bad plug wiring. At this point you were one capacitor away from electrocution. Any failure of that one capacitor could kill you. And kill people they did. Touch the guitar strings with one hand and touch a mic stand with another. Zap. Any guitar amp tech knows exactly what a “death cap” is. SOP with any vintage amp is to rewire them 3 wire, grounded chassis. No matter how valuable and “vintage” it is, that is a non-negotiable modification.
One thing occurs to me. You have a row of 20 odd switching power supplies. These wretched things can retain quite a charge on their inputs when just unplugged. (Enough to give you a painful tingle if you bridge the pings with unwary fingers.) 20 of things is going to be possibly enough of a retained charge that you would see a definite spark if it was somehow provided with a path. Stacked power strips with unknown internal wiring and maybe MOVs providing unexpected paths might be enough to get you there.
Don’t forget 20 common-mode suppression capacitors.