Orphaned Neutral on an AC Service Entrance Conduit (US residential service) - Page 1
Forum section: electronics / general

author: gridleak
author_rank: Contributor
timestamp: December 14, 2017, 05:42:11 am
content: I hope someone here likes to solve mysteries. Eventually I will be calling an electrician to go to the end of the book for whodunit.My typical US residential service has a conduit leading from the meter base to the service panel in the house. If I measure voltage from an extension cord hot blade side to conduit I get 124 volts. That should mean that the conduit is at neutral. However, if I measure ohms from any house outlet neutral blade to conduit I get no continuity. This seems remarkable since the neutral wire is supposed to be bonded to the meter case, and the conduit has a metal fastener to the meter case. Therefore, even if the conduit was not connected to the service panel, there is a conductive path through the meter neutral bond via neutral entrance wire that should connect conduit to neutral in the service panel. All neutrals inside the house checking from outlet to outlet are definitely bonded at 0 ohms between them. Additionally all internal outlet neutrals are grounded. The conduit is not. I can't understand how the conduit is "lit up" with an orphaned neutral. If the conduit is not sharing with house wiring neutral it should be dead. There shouldn't be 124 volts from it to hot. It's as if the legitimate neutral line is not connected to meter case and a second "mystery neutral" line has been brought in from the utility, and tied to the conduit to drive me crazy.

author: Ian.M
author_rank: Super Contributor
timestamp: December 14, 2017, 06:17:07 am
content: You cant measure ohms using a multimeter on a powered circuit. Additionally conduit is known for high resistance problems at joints and fittings and must not be relied on as a grounding conductor. Stop trying to measure anything before the individual breakers in the main panel before you kill yourself and call in a competent electrician!

author: gridleak
author_rank: Contributor
timestamp: December 14, 2017, 10:27:23 pm
content: I think you've hit the nail on the head.Scheduling electrician visit is on the agenda.Thanks!

author: Gregg
author_rank: Super Contributor
timestamp: December 14, 2017, 11:17:21 pm
content: The neutral and ground should be bonded in the panel where the main breaker is located. A ground rod (or alternate permissible ground should also be connected at this point; in certain cases multiple grounding connections are allowed. This should be the only neutral to ground connection on the premises. All metallic conduit and metallic junction boxes, breaker boxes, sub panels etc. should be grounded back to the main ground.For residential services, the neutral should be continuous from the transformer through the main panel (where the ground and neutral are tied) and then on to every circuit that requires a neutral. [There are a few exceptions that are allowed for 120V circuits to return on a ground in an appliance where only the two hot legs (240V) and a ground are wired; but it really isn’t good practice.]The neutral at the power company transformer is usually connected to ground for household services. If the neutral was not connected by the power company, your neutral may be returning on the ground back to the transformer. There should be very little current on the ground at your main panel or anywhere else in your house. A clamp meter used on the ground and neutral wires could show where the problem (if any) exists. Multiple ground to neutral connections can lead to circulating currents and ground conductors inside conduits can have weird current readings if they are connected to both ends of the conduit.As Ian stated, don’t use an ohm meter on live circuits unless you have the right equipment and know what you are doing. A volt meter in this case can easily lead down the wrong rabbit hole. There is very little tolerance for mistakes when dealing with mains power.