Discuss Volt drop on a USB??? in the Electrical Engineering Chat area at ElectriciansForums.net

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Evening all

I’m looking for a little advice here as I have bit of a weird one here.
I got called out to a client to look at some computers that they have reported to have the keyboard and mouse not working and for short I’ll just use KB and M.
So a few other people have had a look at this issue and I’m inclined to think it’s a network issue but I’ll get to that.
I went yesterday but I couldn’t turn anything off whilst they were trading I got L1-N 239 L2-N 242 and L3-N 244 (V) and all seems to be ok. And between all ø they were all 415V
So there is 9 PCs on the circuit and I’ve found it was is a radial there is 26 sockets on said circuit. I’ve had to check the wiring and I’ve found that the first sockets were getting 245v and on the final sockets I got 239v and again nothing to worry about. For now we won’t talk about the measures Zs and I’ll omit talking about it.
I found that the circuit was through crimped and I found that there was some arcing so I removed it and secured the connection I then rechecked my sockets and found I was now getting 246v at the first socket and 242v at the last.
So.... I was there to look at why the PCs KB and M were not responding intermittently and it was even affecting PCs on a different DB nowhere near where I was looking at. (Which again leads me to think it’s a networking issue)
There was a IT engineer that I met on the site yesterday and all he kept saying was that there was earth leakage and my response was the RCBO would trip if that was the case he then said that the circuit needed a clean earth as the PCs are getting too much voltage..... ?

However looking at the panel on the PC their operating voltage states 210-250V

I could understand if there was a problem from the DNO that this issue could be constant so why would this issue jump to different PCs

sorry if I don’t make sense I’m a little tired.
any pointers and advice welcome
 

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This is unlikley to be a supply issue to the pc’s

As you have said, computers are designed to leak a small current to earth and if the cumulative current was enough, then you would have rcd’s tripping intermittently.

It’s possible that the computers are not running the software locally, some office equipment runs on a remote session. So a network issue would cause lagging or no response.
It could be a server problem, or if the server is not on site could be an internet issue.

All you can do is write them a report to say the supply’s to computers are within specification and you can find no fault.

If they particularly want clean earths, you can buy mk sockets with a T shaped earth.
Cpc and functional earth can be separated and run in different cables. However this would be a pricy upgrade and require the plugs changing on every bit of equipment that needs powering from those sockets.
 
A supply issue to the PCs is not going to just cause the mouse and keyboard not to respond. If the supply was really suspect then there would be all sorts of symptoms and issues.

Also, the power supply in a PC is highly regulated, and even if the supply voltage drops a little, the 5V, 12V and 3V3 rails will not really vary.
 
You mention some arcing - it is just possible that interference from that could upset mice & keyboards but it has to be pretty bad (at least on any decent kit).

Many years ago I got an ESD test gun so decided to try it out on my own PC, wound it up to 18kV (max it supported) and discharged it on to my PC, which much to me surprise worked perfectly throughout. Very shortly after that the guy in the next office came in complaining his mouse had stopped working and he had to power-cycle his PC to get it going. I was not the most popular guy that day!
 
You mention some arcing - it is just possible that interference from that could upset mice & keyboards but it has to be pretty bad (at least on any decent kit).

Many years ago I got an ESD test gun so decided to try it out on my own PC, wound it up to 18kV (max it supported) and discharged it on to my PC, which much to me surprise worked perfectly throughout. Very shortly after that the guy in the next office came in complaining his mouse had stopped working and he had to power-cycle his PC to get it going. I was not the most popular guy that day!

I do like a good experiment!
 
Thanks for the responses,
the computers are all networked but I’ve never seen an internet/server problem like this.
I could understand if it was only the computers on the affected circuit that were getting these symptoms but the pc that’s on their pre screening desk and on the EPOS dB which is supplied from the first board and now includes the whole store leads me to think it can only be the server
However the IT monkey (I don’t mean any disrespect but the guy looked like a monkey) kept saying that there was “too much” voltage which is why the fault jumps from one pc to the next as (wait for it) the AC sine wave causes fluctuations. I’ve never heard so much garbage in my life
 
You mention some arcing - it is just possible that interference from that could upset mice & keyboards but it has to be pretty bad (at least on any decent kit).

Many years ago I got an ESD test gun so decided to try it out on my own PC, wound it up to 18kV (max it supported) and discharged it on to my PC, which much to me surprise worked perfectly throughout. Very shortly after that the guy in the next office came in complaining his mouse had stopped working and he had to power-cycle his PC to get it going. I was not the most popular guy that day!
How would yours not be affected though?
 
This sounds more and more like a server issue, EPOS (electronic point of sale)
Requires a good connection to a fast server as it is constantly sending requests to the server for info.
Lots of database lookups and updates constantly running.
This needs a monkey that has evolved past scratching its own arse, try one that can ride a unicycle and juggle at the same time.
 

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