neutral and grounded
- Thread starter kimrichi
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jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
MH newsletter on objectionable current.
http://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/ObjectionableCurrent~20020610.htm
http://www.mikeholt.com/mojonewsarchive/GB-HTML/HTML/ObjectionableCurrent~20020610.htm
- Location
- New Jersey
- Occupation
- Journeyman Electrician
What objectionable current do you have in mind? There are instances where the NEC permits neutral current to flow on other metallic paths.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Say current is flowing on a piece of emt and you touch the emt and another grounded object. Does that answer the question?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Another reason why you want to try and eliminate objectionable current, a fire hazard:
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
The only places I can think of is in 250.140 and 250.142. Any place else?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
250.142 was one that I had in mind.
- Location
- Illinois
- Occupation
- retired electrician
As long as the EMT is a parallel path, that will never be a shock hazard. The only votlage available to drive a shock would the the voltage drop on the parallel paths. The addition of a parallel path reduces this voltage drop.Say current is flowing on a piece of emt and you touch the emt and another grounded object. Does that answer the question?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
And yet it is allowed between the meter and a main panel when using metallic raceway.
- Location
- Illinois
- Occupation
- retired electrician
Another reason why you want to try and eliminate objectionable current, a fire hazard:
As long as the conduit is a parallel path and not the only path I don't see any way there would be enough current flow to cause a temperature rise at a loose conduit fitting.
- Location
- Illinois
- Occupation
- retired electrician
The required bonding of the cable system at the point of entry creates a parallel path for the grounded conductor current.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Interesting so the only reason that objection current is not wanted is ?????
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Agreed, but that graphic depicts what would happen when the neutral is disconnected.
iceworm
Curmudgeon still using printed IEEE Color Books
- Location
- North of the 65 parallel
- Occupation
- EE (Field - as little design as possible)
(edited to add) Adding to comments already made.
Did my best to delete most of the rant.
I don't like MGN, but not for most of the reasons stated here.
First lets look at the regulation (NEC primarily):
Let's start with, Which side of the disconnect are you on?
If you are on the utilty side then grouding the neutral well and often is good and proper.
But on our side of the disconnect, grounding the neutral once is the only safe way.
Unless the system is over 100V, the MGN is again good.
Okay that doesn't make any sense.
Installation specifics:
Most conventional wisdom says that current over the grounding path is dangerous. Humm ... Most arguments are about loose connections, or loose fittings. I'll agree if the connections are poor there will be problems - but that is true MGN or SPG (single point ground)
Lets look at the case of current over a conduit (because of and MGN) - and one is holding the conduit and also touching a grounded object:
Well, if the conduit is bonded as it should be, I say there is no potential difference between the conduit and the ground - so no hazard. Ahhh, but what if the conduit is not bonded as it should be? Well, then the person doing the touching is toast (okay, gets shocked - maybe not dead). What happens if the system is SPG as it should be and the conduit is not bonded as it should be and there is a fault? The person doing the touching is again toasted - likely worse than the above example.
So, why is MGN on our side of the disconnect not acceptable? Cause the code says it's not.
Are there other reasons? Yes, I think so. But we Americans would have to ditch our entire concept of grounding the neutral at residences. And we would have to convice the utilities to drive their own darned ground rods - or give up their concept on MGN.
the worm
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