Isolated ground receptacle

Merry Christmas
Status
Not open for further replies.
G

GG

Senior Member
Location
Ft.Worth, T.X.
What are the codes for isolated ground receptacles as far as the following : Can you use 12/4 MC cable to supply power to an isolated ground receptacle? If you can do you use the green wire to ground the box and green tape on the red conductor to gound the recep strap? Also, where do you land the two ground wires at the panel, do they both go on the ground bar? Im sure I will have more questions about this as it has been several years since I have installed a isolated ground circuit and have basically forgotten all the installation requirments. Thanks.
 
GG said:
Can you use 12/4 MC cable to supply power to an isolated ground receptacle? If you can do you use the green wire to ground the box and green tape on the red conductor to gound the recep strap?
Click to expand...

In most occupancies that will be a volition of 250.119. (You can not remark the red to green)


Also, where do you land the two ground wires at the panel, do they both go on the ground bar?
Click to expand...

Ideally the isolated ground will follow the circuit conductors back through any panels and continue isolated to the panel that has the main bonding jumper. (Either the service panel or the XO of a transformer)
 
Would it be a violation to use the cladding of MC cable with connectors listed for grounding for one ground and the green wire for the other?

We did just that at a dentist's office and the inspector had no problem with it. It was in rural Michigan though and the inspectors there are not always as stringent as the ones in the 'big city'.
 
K8MHZ said:
Would it be a violation to use the cladding of MC cable with connectors listed for grounding for one ground and the green wire for the other?
Click to expand...

No.

Not unless the MC you using has cladding listed for use as an EGC, see 250.118.

That is why Hospital grade AC will work, the armor is suitable for grounding (it has the bonding strip) and it has a insulated green.
 
iwire said:
No.

Not unless the MC you using has cladding listed for use as an EGC, see 250.118.

That is why Hospital grade AC will work, the armor is suitable for grounding (it has the bonding strip) and it has a insulated green.
Click to expand...

It's been a few years but I do remember the bonding strip. I just don't recall the EC I was working for saying it was 'hospital grade'.
 
What is wrong with landing the isolated ground at a sub panel? I realize that the isolated ground must terminate at the main panel I just dont understand why landing it at a sub panel would make any difference. So do they make MC cable with 2 green wires or is it just a cable with 1 green wire whose jacket can be used as a ground, and is this the hospital grade wire someone spoke of? Thank you.
 
GG said:
What is wrong with landing the isolated ground at a sub panel? I realize that the isolated ground must terminate at the main panel I just dont understand why landing it at a sub panel would make any difference. So do they make MC cable with 2 green wires or is it just a cable with 1 green wire whose jacket can be used as a ground, and is this the hospital grade wire someone spoke of? Thank you.
Click to expand...

A true isolated ground goes all the way back to the main panel. The one I did (1999) was at a Central Dispatch center. The MC had a metal strip inside it along with a green wire. We used the green wire for the socket and the MC jacket to ground the yoke and box. The supposed reason was for computers (which I didn't agree with....computers work fine without isolated grounds). In our case, the green wire continued insulated through the panels all the way to the main bonding point. The jacket of the MC cable was connected to the exposed metal and the receptacle yokes via listed connectors.
 
K8MHZ said:
The one I did (1999) was at a Central Dispatch center. The MC had a metal strip inside it along with a green wire. We used the green wire for the socket and the MC jacket to ground the yoke and box. The supposed reason was for computers (which I didn't agree with....computers work fine without isolated grounds). In our case, the green wire continued insulated through the panels all the way to the main bonding point. The jacket of the MC cable was connected to the exposed metal and the receptacle yokes via listed connectors.
Click to expand...


If you were doing this your use of the cable armor to ground the box/yoke was a violation. Back then the armor of MC was not a listed EGC and could not be used in the manner you've described.
 
Not to be redundant (no pun intended) but the cable Bob (iwire) cited (HCF-AC) is the correct cable to use. It contains the shunt wire spiraled inside the metal jacket creating a redundant ground. The metal jacket inserted into a proper connector provides a means of grounding the metal box and any other metal parts and the green wire inside the jacketed cable lands on the ground terminal of the ISO receptacle to provide isolated grounding for the device plugged into it.

I don't know this to be a fact but during one of my CEU courses an instructor told us that one of the reasons for isolated grounds for computer equipment is to reduce the possibility of harmonics. Also, the next time you strip a length of MC or HCF cable take notice of the way the wires inside are spiraled. They'll twist one way for about 3-4' and then back the other way for 3-4' and so on. Another attempt to reduce harmonics. If anyone else knows differently please say so.
 
goldstar said:
I don't know this to be a fact but during one of my CEU courses an instructor told us that one of the reasons for isolated grounds for computer equipment is to reduce the possibility of harmonics. Also, the next time you strip a length of MC or HCF cable take notice of the way the wires inside are spiraled. They'll twist one way for about 3-4' and then back the other way for 3-4' and so on. Another attempt to reduce harmonics. If anyone else knows differently please say so.
Click to expand...


Harmonics have nothing to do with IG systems or the twists in a cable. Regarding the spiraling, you would have to show me that. :confused:

I've skinned thousands of feet of AC and MC cable and never saw spiral reversal every few feet.
 
infinity said:
I've skinned thousands of feet of AC and MC cable and never saw spiral reversal every few feet.
Click to expand...

For a while we where getting MC like that, I had no idea why and it really was a pain to work with when cutting in panels. I also have not seen it again for at least a year or two.
 
infinity said:
Harmonics have nothing to do with IG systems or the twists in a cable.
Click to expand...
Don't be so sure ! :smile: What do you believe is the reason for the isolated ground ?
Regarding the spiraling, you would have to show me that. :confused:
I've skinned thousands of feet of AC and MC cable and never saw spiral reversal every few feet.
Click to expand...
OK. How about this for a testimonial :
iwire said:
For a while we where getting MC like that, I had no idea why and it really was a pain to work with when cutting in panels. I also have not seen it again for at least a year or two.
Click to expand...
benaround said:
I used some just the other day, thought the shop got some ' bargain ' rolls of the stuff.
Click to expand...
To quote the M & M's commercial "So It Does Exist !!!" And, I'm not going crazy. I think maybe the cable mfrs. were going through a testing period and were trying to kill 2 harmonics birds with one stone. But, then again, I've been known to be wrong.

Regards,

Phil
 
infinity said:
Regarding the spiraling, you would have to show me that. :confused:

I've skinned thousands of feet of AC and MC cable and never saw spiral reversal every few feet.
Click to expand...

I skinned some last week and noticed the reverse in the sprial. I'd never seen that before. It really does exist though, I've got a roll on the truck I'll try to take a pic for you.

I don't think it's for harmonics or increased data transmission rates though :) I think it's just a change in a machine at the factory that makes the stuff. At one factory. That's why not everyone has seen it. I think it's recent change either way...
 
goldstar said:
Don't be so sure ! :smile: What do you believe is the reason for the isolated ground ?
Click to expand...

Current flowing on grounding conductors when electronic equipment is interconnected with cables that also connect the EGCs between equipment.

It is not about harmonics.
 
jerm said:
At one factory. That's why not everyone has seen it. I think it's recent change either way...
Click to expand...

I think there is one particular manufacturer that does the "reverse twist" on all their MC...I think it's United Copper Industries, but I'm not 100% sure.

I do remember working with a batch of UCI MC cable that was literally soaked with oil, not just the usual thin film that's on it.
 
iwire said:
For a while we where getting MC like that, I had no idea why and it really was a pain to work with when cutting in panels. I also have not seen it again for at least a year or two.
Click to expand...

I've seen romex like that in 14-3 and 12-3, but not -2.
Can't say that I've seen MC like that.
 
iwire said:
Current flowing on grounding conductors when electronic equipment is interconnected with cables that also connect the EGCs between equipment.
Click to expand...
OK. I can buy into that.
It is not about harmonics.
Click to expand...
I'll start preparing the crow but I'm not ready to sit down to dinner yet until we figure out what the reverse twisting is for.:D
 
Status
Not open for further replies.
Top