Residential furnace grounding

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muskie

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Received a fax from a local heating contractor, that a furnace needs an isolated ground wire from furnace to the panel, also that a conduit is not a ground wire. Also stated that the furnace cabinet MUST HAVE AN UNINTERRUPTED or UNBROKEN GROUND per NEC ANSI/NFPA 70-2002
I can't find an article in NEC pertaining to this. Has anybody else had this happen? :?:
 
Reply to him that you would like the EXACT code section. Not just the article. I'd be interested to see what he comes back with.

He is right about one thing - a conduit isn't a ground wire. A conduit is a conduit, just like a heating duct isn't a condensate drain. :)
 
I think he's trying to say that he wants a ground wire installed with the conductors in the pipe and not to use the pipe as EGC.
Maybe there is some new computer type controls with the furnace that require a equipment ground wire.
Just my guess
 
Ask him for the mfr's installation instructions. Most of us would be interested in knowing what brand furnace is "calling for" an isolated ground.
COuld be something new or...
 
"a conduit isn't a ground wire"
Not quite true. 250.118 lists the allowable equipment grounding conductors, which includes RMC, IMC, EMT, AC cable,...
Also there is no requirement in 250 for the EGC to be insulated.
 
The "unbroken" ground perplexes me too. I ran the wires for my heat pump air handler and then noticed that "unbroken" requirement in the furnace install instructions. I don't know what unbroken means -- it didn't say unspliced, and certainly a broken ground is of no value...

I also ran a #8 EGC along with the two sets of #6 branch circuit wires in the conduit. Even though the NEC says #10 is large enough, the install instructions said to use #6.

I terminated the #8 EGC in my junction box near the furnace with a small grounding bar. The furnace installer didn't use the length of #8 I left him and put a #6 from the junction box to the furnace. The installer didn't complain about the grounding bar.
 
FC nailed it. Most likely the unit is computer controlled and without the unbroken ground back to the panel, the computer will lose memory. However this is not an NEC requirment just a manufactor's requirment. We install a lot of drycleaning and laundry equipment that requires the same. Most of our ground connections on certin drycleaning machines require a driven ground at it's location. At first I thought this was a lot of overkill, but without the driven ground the unit loses memory. Also, like any other computer, it's best to supply it with an isolated ground, which is what they're really asking for.I could be wrong,, but
 
Electrick One said:
FC nailed it. Most likely the unit is computer controlled and without the unbroken ground back to the panel, the computer will lose memory. However this is not and NEC requirment just a manufactor's requirment. We install a lot of drycleaning and laundry equipment that requires the same. Most of our ground connections on certin drycleaning machines require a driven ground at it's location. I could be wrong,, but chances are,,,,
Click to expand...



I hope thats a supplementary and not your system ground.
 
Electrick One said:
F Most of our ground connections on certin drycleaning machines require a driven ground at it's location. I could be wrong,, but chances are,,,,
Click to expand...

Can you explain what benefit this ground rod will produce? I certainly hope you are bonding this ground rod to an the branch circuit EGC! if not, you have an extreme hazard on your hands!
 
Sorry I didn't make myself clear. The drycleaning unit requires a supplemental ground in addition to the EGC. without it the unit's computer will lose memory. I don't know why,, just does

But I think the heating unit in question just requires an isolated ground.
 
The drycleaning unit requires a supplemental ground in addition to the EGC. without it the unit's computer will lose memory. I don't know why,, just does
Click to expand...
We are very obsessed with the "whys" around here. What you're saying doesn't make sense. With the description given, it sounds like defective equipment. :?
 
" require a driven ground at it's location.
I have a study from the EPRI that shows adding a ground rod at a equipment makes the noise worse.
Mike Holt and myself would like to see a copy of those instructions.
Perhaps there is an instruction manual I could download as a PDF, can you check and see if there is and provide a link?
 
Electrick One said:
Sorry I didn't make myself clear. The drycleaning unit requires a supplemental ground in addition to the EGC. without it the unit's computer will lose memory. I don't know why,, just does

But I think the heating unit in question just requires an isolated ground.
Click to expand...


I think that you meant supplementary ground. A supplemental ground is used to supplement the water pipe electrode on a service. A supplementary ground, also called a signal reference ground, would be used for sensitive electronic equipment as you've described.
 
Supplemental ground is what I call a time and materials electrode, its not required.
An isololated ground rod is a violation of the NEC
 
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