Can an open ground occurring in an APC product cause static discharge?

[Anonymous user]

I have had a small music studio for about four years, in my home, in a carpeted room, and I have not had any problems with static electricity until now. The relative humidity in the room averages 50%, so I don't suspect that is contributing to the problem much. I hear a quick 'zap' occasionally when I am playing my electric piano. I suspect that this is happening because the sustain pedal is sitting directly on the carpeted floor and I use the pedal quite a bit.

I installed a static dissipative mat and I still hear the 'zap' at random times. Really perplexed, I disconnected everything from the system except one keyboard, the MacBook, and the FP10 audio interface. I played for hours, using only headphones, and heard no zap. I then plugged in the monitors and eventually heard the zap again. But, the volume of the zap is always the same, regardless of the volume setting on the monitors and/or FP10.

So I took my trusty Greenlee circuit tester and plugged it into every wall outlet in the room. The lights indicated correct power and ground in all cases. Then I plugged the tester into my APC Back-UPS ES 350 battery backup/surge protector. And Lo and Behold (does anybody really say that any more?), when I plugged the tester into one of the outlets on the battery backup/surge protection side, both lights indicating a good connection came on -- and a few seconds later, only the center light shined. The legend on the tester labeled that condition "OPEN GROUND". After 10 seconds or so, the other light came back on. I watched the tester for about 30 minutes, and the light went off and on a few more times.

So, is there an electrician reading this post that could confirm or deny that this could be the source of the zap?

The APC was plugged into the same AC wall outlet as my Furman power conditioner, so could that also contribute to the problem, i.e. does proximity have a bearing on this problem?

[Anonymous user]

I plugged a multimeter into the APC's outlet that is suspect. It initially read 117 volts, but after 10 seconds it dropped to 82 volts. A few seconds later, it read 117.

Could this cause the static noise I heard? I'm going to reconnect everything ( except the APC) and test, test, test.

Message was edited by: agreenberg19

[BillP]

is it a true RMS voltmeter? did you test it when you put the UPS on battery? i guess can you clarify step by step some steps to replicate what readings you are seeing?

i ask because this sounds a lot like what is here:

http://www.apc.com/site/support/index.cfm/faq/ -> search for FA157483

at the time i post this though, ugh, it appears apc.com is experiencing issues 😞

and i don't know if it is related just yet but we have this information regarding a "floating" ground and it just came to mind when reading your issue:

___________________________________________________________________________________

Although many APC UPS’s have a voltage present between Earth and Neutral while unit is on battery it must be pointed out that these units comply with EN and CE standards.

This issue can be explained as follows:

When the unit is online it is obviously has a Neutral from the supply and in the standard TN network, the Earth and Neutral are at the same potential due to the fact of both are connected at the main distribution board.

However when it goes on battery or should the supply be disconnected, both poles will be disconnected from the supply thus creating an IT system. The supply has then no reference to the earth so the first fault is not a safety hazard.

Types of Wiring Networks:_


TN: System where Neutral an Earth (Ground) are connected. There are variations of this system, see below.

TN-C: System where Neutral an Earth (Ground) are common throughout the system.

TN-S: System where Neutral an Earth (Ground) are separate throughout the system.

TN-CS: System where Neutral an Earth (Ground) are common between substation and the building and separate down stream from the main distribution board. This is one of the most common types of electrical networks.

TT: In this system the Neutral (star-point of the transformer) is connected to Earth (Ground) but there are no further connections between Earth and Neutral downstream. The Earth of the building is connected directly to earth by means of an earth-spike or earth-plate. This system is also sometimes known as direct earthing and needs earth leakage protection.

IT: This system is different to the other systems as no part of the secondary side of the transformer is connected to Earth so that there is a floating earth in such systems. As there is no return path this system is very safe if installed properly. It is used in hospitals, mines and other special areas. It should have Earth Leakage Monitors installed as protection.

[Anonymous user · Accepted solution]

I'm afraid all that is way over my head. I am a retired computer programmer and an amateur musician, so I basically know how to turn electrical appliances on and off.

I just wanted to know if that change in voltage could cause a static discharge that would be audible in my studio. I have removed the APC unit and, so far, have not experienced any static 'zaps'.

I do appreciate your input.

Alan