Two seperate Electric Services in one house causing problems.

[catsfan09]

We have a client that has two independant electric panels and services in their house after adding on a significant addition. They have a shared electronics rack for the entire house and are experiencing grounding issues due to some of the electronics living on one service while others are on the other service. The electrician has supposedly bonded the two panels together which hasn't solved the problem. There must be a solution and any help/advice would be much appreciated!

 

[pwrengrds]

There is nearly always a solution, to determine it you need to know what the problem is.

What kind of grounding issues are they having? How was the systems bonded together?

Have you checked to see if they are bonded together? ie checked the bonding with an ohm meter.

 

[itsmoked]

A good reason to avoid two services..

What kind of problem is he experiencing?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

I have a gut feeling that we may have the wrong solution to the wrong issue.
What is a

shared electronics rack

and why is it an issue.
Start by describing the issue. What is interfering with what? Where are the supposed harmonics coming from?
It sounds as if someone who is not familiar with distribution systems has made a bad guess that grounding is causing issues. Then a correction was made but the issues did not go away, so what is wrong with the solution?
This may be a classic case of misdirection or BSiBSo (Bogus Suggestions in equals Bogus Suggestions out).

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Hmm, why do I think that B.S. might some other meaning...?


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[catsfan09]

Hi guys!
Sorry that I did not reply as you all posted. Here is a brief snapshot of the problem.

The customer added onto their house and added a new service (new panel, meter head, ect) to the entire addition. The old section stayed on the old service. When construction was going on his electronics guy pulled Coaxial and Category wire to monitor locations in the old house to be connected to a matrix switch in the new part of the house. Feeds were ran to monitors in the new house as well. All monitors in the new section on the new service have crystal clear pictures(All of the electronics and cable components in the rack are powered via the new service). All monitors in the old section have scrolling hum bars from the cable system as well as a large purple bar that scrolls at a different speed.

We can isolate the cable to get rid of the hum bar from the cable system and have used jensen transformers to get rid of the purple hum bar. The only other way we have eliminated the purple hum bar is to disconnect all displays, power sources ect from the new section and powering the components via an extension cord from any circuit in the old section. Trying any other circuit in the new section brings the problem back.

Seems to be a grounding or some sort of power issue and I will be the first to admit that I do not know a lot about AC power and high voltage. That is why I am here! The electrician that did the installation has no clue when he looks at the display and we talk to him about the problem.

Thank you all for your time and effort.

 

[rbulsara]

If this is in the USA, a second meter in a house is not permitted by NEC. Is this a legal installation? Was a permit obtained? You may want to check that first.

Rafiq Bulsara

http://www.srengineersct.com

 

[catsfan09]

Hmm, you may be onto something here! I have not laid eyes on the second meter head but have been told that they are two seperate services. Both panels are rather large and I am not sure if there is a limit to how large a sub panel can be or how these two panels would share the same meter. Let me find this out for sure and get back to you guys. If there are two meters and this is illegal then I have my answer already. If you could send me a copy of this section of the code or at least where I can find it in the book that would be great!

Background on myself: I have a B.S. in Computer Science hence computer after my handle not electrical !

 

[rbulsara]

Look up NEC 230 , the article on services.

Rafiq Bulsara

http://www.srengineersct.com

 

[ghostbuster7]

We had a very similar problem with a smart home several months ago.Your signal co-ax grounds etc. are carrying neutral imbalance current between these services and causing this distortion to occur.In our case, we rederived our system neutral and the problem disappeared.Good Luck

 

[telecomguy]

Sounds like a ground loop. Check out

http://www.everyspec.com/NIST/NIST+-+FIPS/download.php?spec=FIPS_PUB_94.003307.pdf

(thanks to 'busbar' for posting this document in another thread recently)

Pages 41 & 42 seem to depict your problem and a solution is provided.

-tg

 

[catsfan09]

Thanks for the article telcomguy! Was very helpful. And yes the house has two separate meters and services. Not sure if it was a legal installation or not.

 

[waross]

Issue #1 Two services.
Issue #2 Bridging neutrals. If, as has been suggested, the coax shield is carrying neutral current between the panels, this could be the cause of the problems. No matter if there are two panels or a main panel and a sub panel, (as per code). A neutral current will cause a voltage drop on the neutral. It would not be uncommon for the neutrals of the two panels (either main and sub panel or two services) to have different neutral voltage drops. The difference in potential between the neutrals will cause a current to flow in a any sheath or conductor that is bridging the neutrals. The current will be the voltage difference divided by the 60 Hz impedance of the sheath or conductor. Running more and larger grounds and neutral jumpers between the panels may reduce the bridging current in the sheath but will never eliminate it completely (Unless the jumper has zero impedance. Not likely)
The solution may be to supply all electronics from one panel. Supplying some units from a main panel and some from a sub panel may be troublesome. Another issue with bridging grounds/neutrals is fault currents. In the event of a fault fed from one panel, the neutral/ground jumper will carry some of the fault current and the coax sheath will carry its share of the fault current. The sheath share of the current may not be enough to damage the sheath but it may result in damae to electronic circuits.
Neutrals are not the same as grounds, even though they are often at the same potential. If you have two services properly installed, the neutral will be grounded at both services and a jumper will be both a ground jumper and a neutral jumper.
If you have a main panel and a sub panel it gets more complicated. Is the coax sheath bridging the neutrals or bridging the grounds? Is the grounding jumper that the electrician installed between the ground bars or the neutral bars? Is the sub panel wired properly (ground isolated from the neutral) or is the neutral connected to ground. That is a code violation in most sub panels.
Bottom line;
Pick a panel to feed all the electronics from. Check each device with an extension cord from the feed panel. Remember to check for junction and/or boxes originally fed and grounded from the other panel. Best to install new outlet boxes fed only from the selected feed panel and eliminate any contact with boxes fed from the problem panel.
BTW, thanks for the clear explanation of the problem.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[PHovnanian]

Check exactly how the two systems are grounded and bonded. It is possible for two services to coexist in one occupancy. Although the practice may not be legal in residences, it is done in commercial/industrial occupancies. With careful design, ground loops can be avoided. But this might be something that a residential electrician will overlook.

 

[busbar]

Kind of a cutthroat solution, but maybe it’s time to replace some copper interconnecting data cables with fiber.