Potential Electrical Hazards Associated with Replacement of Water Meters or Water Mains

Electrical Safety Authority (ESA)
October 2013

Background
During the replacement of a water meter for a local municipality, it was noticed that arcing was occurring on the domestic metallic water pipe when it was broken to facilitate the installation of a new water meter. The electrical system of the building was utilizing the incoming domestic water pipe system as the ground electrode. The Ontario Electrical Safety Code (OESC)
Rule 10-700 allows a metallic water piping system installed 600mm below grade and extending no less than 3m out from the building to be utilized as a ground Electrode.

Reason
In some instances with the degradation of the neutral terminations of the incoming supply system it is possible that the return path of electricity may utilize the grounding conductor and potentially the water main as a return path to the utility supply as shown in Diagram F1. 

CAUTION
An indicator that service neutral terminations may be degrading is indeed the arcing of the grounding conductor at the electrode or the breaking of the electrode in mid path as may occur when the water meter is replaced or the incoming domestic water pipe is broken.  This arcing on the water main is indicative of a more serious problem with the electrical system which requires investigation by a Licensed Electrical Contractor (LEC). The LEC will need to determine if the electrical wiring in the building is compliant with the OESC. The supply authority should only be notified after the LEC has determined the arcing is from external sources.
 
Extreme care must be taken when replacing water meters or incoming domestic water mains. The potential of an electrical shock may be realized under conditions of service neutral failure.

Read the full report online at http://www.esasafe.com/assets/files/esasafe/pdf/Bulletins/13-03-FL.pdf