Is isolated grounding really required

[kevinware]

I have been asked by a member of management in the building I work if I would install some receptacles in his basement. Now the catch is that these receptacles will be used for audio equipment. (Amplifiers, mixers and the like)
I have not seen the basement yet but just thinking here, this equipment is probably expensive. This isn't a professional studio or anything so I can't see a need for any type of balanced power system and if I am reading 647.3 correctly I am not permitted to install this type of system in a single family residence, please correct me if I am misinterpreting 647.3. The way I was thinking of handling this is I was going to install each duplex receptacle on a dedicated circuit and have the owner invest in some sort of power conditioning unit. I am thinking of Romex as the wiring method but I may need to use some EMT and mounted some of these receptacles to the concrete foundation wall 334.15(B), like I said I'm not sure yet. Will see the basement tomorrow. Anyway, Would it be a better ideal to have these circuits be an isolated ground type? If I am bonding the standard receptacle to the metal box on a dedicated circuit is it still possible to have noise on the EGC? What are your opinions?

Thanks,

Kevin

 

[bphgravity]

Re: Is isolated grounding really required

I'm not a big fan of altering code minimum installtion requirements for the purpose of special equipment. I feel it should be left up to the product manufacturers to provide a way for their equipment to work properly on any electrical system that may be utilized.

I'm also not sold on the whole ISO ground theory. It doesn't make sense to me...

 

[celtic]

Re: Is isolated grounding really required

Originally posted by kevinware:
... these receptacles will be used for audio equipment. (Amplifiers, mixers and the like)
I have not seen the basement yet but just thinking here, this equipment is probably expensive.

I would have a look at both the basement and equipment BEFORE I got all excited about 647, Isolated grounds and power conditioning.


You are correct in that 647 is not for residential applications.

A 1x4 is a cheaper method for mounting Romex to a concrete foundation wall - how does 334.15(B) apply to foundation wall?? - surely this will not be exposed?. Take a look at 334.12(A)10 (2002) or 334.12(B)4 (2005)

Again, have a look at what he has and what he plans to use - we'll still be here

 

[kiloamp7]

Re: Is isolated grounding really required

Generally - a properly bonded & grounded (earthed) electrical system will do the job just fine & is simple & straightforward.

Forget "isolated ground" unless you have a very good technical reason. IMO you will probably not have a good reason.
Art. 647 is a specialized 60/120V. system.

 

[kevinware]

Re: Is isolated grounding really required

I only stated 334.15(B) because I wanted to protect the romex from being damaged. (just incase)Is there a better way?? Please instruct me!!

Edit to add: I thought 334.12(B)(4) was to keep romex from being the wiring method used in a wet or damp location. I'm not trying to be difficult but I guess I'm not seeing something. I am just using the EMT to protect the romex. Is my using romex not permited? Should I set a box up in the joist and come off the box with my EMT with THWN/THHN conductors?

[ February 24, 2006, 01:26 PM: Message edited by: kevinware ]

 

[celtic]

Re: Is isolated grounding really required

Originally posted by kevinware:
I only stated 334.15(B) because I wanted to protect the romex from being damaged. (just incase)Is there a better way

Well, 334.15 is for EXPOSED work...
Generally speaking, inside a wall is not considered exposed

Originally posted by kevinware:
Edit to add: I thought 334.12(B)(4) was to keep romex from being the wiring method used in a wet or damp location. I'm not trying to be difficult but I am just using the EMT to protect the romex. Is my using romex not permited? Should I set a box up in the joist and come off the box with my EMT with THWN/THHN conductors?

The proviosions of 334.12(A)10 (2002) or 334.12(B)4 (2005) indicate "Where exposed or subject to excessive moisture or dampness " - a basement wall quallfies as damp(100) (generally speaking). The 1x4 on the foundation wall keeps the Romex off the wall - and is much cheaper than EMT (material) and snaking the Romex down the EMT (labor).
Protecting the romex, while admirable, is not the requirement here - The cable shall be protected from physical damage where necessary by conduit(334.15) - keeping it away from dampness/moisture is the requirement(334.12)...unless , of course, the romex is exposed(334.15). Even in a damp/moist location Romex can be used - provided the romex is not subject to that moisture/dampness ~ hence the 1x4. When the walls get framed out, a CJ6 would keep the romex off the surface of the exterior wall - and are even cheaper than a 1x4 and anchors.

You could do this thing a variety of ways...AC, MC, Romex, EMT, RMC....it all depends how much the HO wants to spend $$$...and how you follow the code book/local laws.

 

[colosparker]

Re: Is isolated grounding really required

An electrical engineer explained to me that the computers and electronics in use today use a higher switching mode than in the past. He stated that isolated grounding for this type of equipment is obsolete and a waste of money. A dedicated circuit along with a small UPS should be more than adequate for audio equipment in a residence. The UPS will protect the bosses expensive audio equipment from objectionable power transients. The dedicated circuit will insure there are no objectionable loads on the circuit which could cause noise, ie: flourescent ballasts, motors, etc.

You can never go wrong with EMT,, unless of course you don't know how to bend the stuff and support it properly. O an side note: Whenever the management asks for my help on electrical matters in their home, I tell them I don't do side work.