120volt panelboard with "common neutral" branch circuits.

[pnunley]

I was working in an OR in a hospital where I was troubleshooting breakers tripping intermittently for no apparent reason. Upon taking the cover off of the panelboard fed from a 120volt isolation transformer I noticed two items of concern to me.

1. The electrician installed two circuits in each conduit feeding receptacles using a common neutral. By definition this is not a multiwire branch circuit.
2. The IG receptacles were fed with two grounds. One from the isolated ground bar and one from the equipment ground bar. Both were tied together at each receptacle location.

It is my understanding that there is the possibility of an overload on the neutral in #1. The purpose of the IG is defeated by tying them together at the device location in #2. Am I correct in both assumptions?

Also, considering the situation is there any reason that they are getting nuisance tripping on the IG receptacle circuits?

Thank you!

 

[infinity]

Incorrect response.

 

[roger]

I was working in an OR in a hospital where I was troubleshooting breakers tripping intermittently for no apparent reason. Upon taking the cover off of the panelboard fed from a 120volt isolation transformer I noticed two items of concern to me.

1. The electrician installed two circuits in each conduit feeding receptacles using a common neutral. By definition this is not a multiwire branch circuit.

There is not a neutral in an Isolated Power system

2. The IG receptacles were fed with two grounds. One from the isolated ground bar and one from the equipment ground bar. Both were tied together at each receptacle location.

IG receptacles would be a violation of 517.13 and as an aside, 517.16 has been removed in the 2011, it really was never allowed even though it was in there.

It is my understanding that there is the possibility of an overload on the neutral in #1.

You have two legs at 60 volt each so I don't know what a neutral is doing. You should have an Orange and Brown landed on the receptacles, see 517.160.

The purpose of the IG is defeated by tying them together at the device location in #2.

You are corcect in your assumption of question #2 which would make it illegal in Patient Care Areas.

Also, considering the situation is there any reason that they are getting nuisance tripping on the IG receptacle circuits?

Thank you!

I don't think it would be due to your questions.


Roger

 

[infinity]

There is not a neutral in an Isolated Power system
IG receptacles would be a violation of 517.13 and as an aside, 517.16 has been removed in the 2011, it really was never allowed even though it was in there.

You have two legs at 60 volt each so I don't know what a neutral is doing. You should have an Orange and Brown landed on the receptacles, see 517.160. You are corcect in your assumption of question #2 which would make it illegal in Patient Care Areas.

I don't think it would be due to your questions.


Roger

So this is an isolated power system?

 

[Dennis Alwon]

So this is an isolated power system?

I believe in OR rooms they must use isolation transformers

 

[roger]

So this is an isolated power system?

Best I can tell from the OP's second sentence and it would be common in an OR.

Roger

 

[roger]

I believe in OR rooms they must use isolation transformers

Dennis, that is correct in NC and some other states but, I think some states have gotten away from it and allow GFCI protection. They are an option as far as the NEC goes.

Roger

 

[Dennis Alwon]

Dennis, that is correct in NC and some other states but, I think some states have gotten away from it and allow GFCI protection. They are an option as far as the NEC goes.

Roger

Interesting because my daughter -in- law who is in school for anesthesiology nursing in Ashevile just sent a powerpoint on this showing an isolation trany. I assumed it was NEC--

Roger I did not notice this in the amendments of NC so how is this being enforced?

 

[roger]

Interesting because my daughter -in- law who is in school for anesthesiology nursing in Ashevile just sent a powerpoint on this showing an isolation trany. I assumed it was NEC--

Roger I did not notice this in the amendments of NC so how is this being enforced?

Dennis, it's a NC DHSR requirement.


Roger

 

[texie]

Interesting because my daughter -in- law who is in school for anesthesiology nursing in Ashevile just sent a powerpoint on this showing an isolation trany. I assumed it was NEC--

Roger I did not notice this in the amendments of NC so how is this being enforced?

Small world....I have a son in N.A. school as well. Of course when he took that part of his training he called me trying to get an understanding of the concept. I think in most places now it is old school and they are going more and more to GFCI.

 

[pnunley]

Thank you for the replies so far.

My understanding of NEC 517.61(A)(1) is that if flammable anesthesia is used then you are required to have an isolated power system.

I recommended that we correct all the IG issues by separating them at each device. Also, pull an additional neutral (grounded conductor) through each conduit to take out the possibility of overloading the "neutral".

I believe the nuisance tripping is due to the equipment being used but I can't get it to trip while I am there. :-(
I wasn't sure if I was missing something.

Thank you

 

[pnunley]

There is not a neutral in an Isolated Power system
IG receptacles would be a violation of 517.13 and as an aside, 517.16 has been removed in the 2011, it really was never allowed even though it was in there.

You have two legs at 60 volt each so I don't know what a neutral is doing. You should have an Orange and Brown landed on the receptacles, see 517.160. You are corcect in your assumption of question #2 which would make it illegal in Patient Care Areas.

I don't think it would be due to your questions.


Roger

Roger,

The OR was completed under the 2005 NEC which allowed for the IG receptacles in 517.16. However, you are correct and the 2011 NEC does not allow for this so I will not change this and keep them bonded together.

 

[roger]

Thank you for the replies so far.

My understanding of NEC 517.61(A)(1) is that if flammable anesthesia is used then you are required to have an isolated power system.

Flammable anesthesia is no longer used in most modern countries. It is still in the NEC because of the fact that some third world countries use it and they also use the NEC

I recommended that we correct all the IG issues by separating them at each device.

That is exactly what you don't want to do, once again, see 517.13 and the requirment for redundant grounding, not isolated grounding.

Also, pull an additional neutral (grounded conductor) through each conduit to take out the possibility of overloading the "neutral".

If you actually have an Isolated Power System as you said in your openning post there is no neutral involved.

Roger

 

[roger]

Do the panelboards have Line Isolation Monitors (LIM's) and are the conductors XHHW?

Roger

 

[pnunley]

Flammable anesthesia is no longer used in most modern countries. It is still in the NEC because of the fact that some third world countries use it and they also use the NEC

OK I appreciate this since I thought N2O was still used in some circumstances and flammable.

That is exactly what you don't want to do, once again, see 517.13 and the requirment for redundant grounding, not isolated grounding. If you actually have an Isolated Power System as you said in your openning post there is no neutral involved.

Obviously I do not understand fully the idea/engineering of an isolation transformer. I gather from this statement that the installation complies with the NEC as is other than the fact that under the 2011 we can no longer use IG receptacles.
Roger

Thank you for your input and patience.

 

[pnunley]

Do the panelboards have Line Isolation Monitors (LIM's) and are the conductors XHHW?

Roger

There are eight ORs and some do and some don't. Specifically the ones that are tripping the breakers do not.

 

[roger]

Thank you for your input and patience.

No problem

There are eight ORs and some do and some don't. Specifically the ones that are tripping the breakers do not.

Now that does sound odd. Typically there would not be a mix of systems in these spaces. I wish I could be of more help but something is different here and I may be leading you down a wrong path.

Roger