enireh
Senior Member
- Location
- Canyon Lake,TX
in a nutshell, why was 3 wire systems ok in the past but now its important to have 4 wires? what is the advantage?
4 wires to sub panel
- Thread starter enireh
- Start date
- Status
- Occupation
- Licensed Electrician
Are we talking about sub panels to a remote building?
enireh
Senior Member
- Location
- Canyon Lake,TX
sub panel
sub panel
sub panel
same building, a residence and if it was a remote building how would that differ?
- Occupation
- Licensed Electrician
It has never been allowed to run three wires to a sub panel within the same building, although enforcement was not always uniform.
Before 2005 it was legal to run three wires and re-bond the neutral at a separate structure if there was no other conductive path between the two buildings.
Before 2005 it was legal to run three wires and re-bond the neutral at a separate structure if there was no other conductive path between the two buildings.
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
As far as I know, it's always been required in the same building.
They used to allow it in a separate building if there were no metallic paths between the buildings.
The rule is to keep objectionable current from flowing on the normally non current carrying metal objects that may be in the path. Also, if the neutral were to be lost/disconnected, there would be no path back to the source to trip a OCPD.
ETA: My "Action" isn't as fast as Dave's!
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
The major reason is because the neutral has current flowing on it, which means there is voltage drop or voltage differential between different parts of it. When you bond things to the neutral in multiple places, you thus have touchable metal things at different potentials. If we bond things together with a 4th conductor (or 3rd if its a 120 circuit) that doesnt normally carry current, then everything stays at the same potential (except for very brief periods during a fault).
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