publicgood
Senior Member
- Location
- WI, USA
Agree, but maybe it should apply. 2 cents
240V bathroom heater, now need a neutral for electronic timer switch...
- Thread starter publicgood
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Agree, but maybe it should apply. 2 cents
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Quite honestly I thought that rule never belonged in NEC in the first place. That is design issues not safety issues.
publicgood
Senior Member
- Location
- WI, USA
Is not the intent to avoid normal flowing unbalance (neutral) current on an equipment ground? Known as objectionable current.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Yes, and if you install something that requires a grounded conductor then you must install a grounded conductor. IIRC some of this came about because there were devices out there that were using the EGC when they probably should have been identified as a grounded conductor connection, and they were listed for use like that at the time.
NEC claims it is not a design manual, yet has taken the "design manual" route when it tells us we need to install the grounded conductor even if the load doesn't require it.
Not saying it isn't good practice to install grounded conductor at switches that are likely to get changed to a device that needs a grounded conductor.
Quite a few changes in NEC have encroached the "not a design manual" claim in the past 30 years IMO.
eBay?
publicgood
Senior Member
- Location
- WI, USA
Point of clarification, the NEC is a design manual. It just isn’t a design manual for untrained persons. See 90.1
- Occupation
- Licensed Electrician
No. That's not what it says.
It says that the code is not intended as
a) a design specification
b) an instruction manual for untrained persons.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
My understanding is that when 'UL listed' devices used the EGC as a 'neutral', that the current levels were lower than the UL specification for permitted insulation leakage.
In some ways this becomes a question of intent: if the insulation leaks (which it does) then some current will flow on the EGC, but you don't intend it. But if you wire something to the EGC then you _intend_ for the EGC to carry some current.
The EGC will _always_ carry some current, if only because of capacitive coupling. The question is: how much do you allow, and do you allow it to be intentional?
IMHO we should permit intentional use of the EGC as a current carrying conductor, but the allowed current should be a fraction (10%? 20%) of the current permitted for unintentional leakage, and total current should not exceed that permitted for unintentional leakage.
If I did my math right, 100 feet of 12-2 NM carrying a 240V circuit will see something like 150 microamps on the EGC. I don't know what the UL permitted leakage would be, nor the similar value for a switch.
But 25 microamps at 240V is 6 milliwatts, enough to run many control circuits. I don't see any problem with permitting a switch to 'dump' 25 microamps to the EGC.
-Jon
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
And I probably was somewhat incorrect also when I said "design manual", though I could say I was summarizing in my own words instead of quoting what NEC says.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I don't see 25 microamps on EGC as a problem either. Having a MGN system on the utility side of the service can introduce more troubles then this pretty easily.
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