Page 7 - 2020 May E-issue

Technical Corner

This month we will go over the changes in NEC 555.3 which lists the requirements for Ground Fault Protection
for marinas, boatyards, commercial and non-commercial docking facilities.

We will be comparing the NEC 2014 requirements to the NEC 2017 requirements.

There are 2 main points Id like to write about.

The first point being the decreased threshold of ground fault protection from 100mA to 30mA in the latest code. A
30mA threshold certainly is an acceptable level to prevent a majority of electrical shock drowning incidents while
remaining practical enough to minimize unnecessary tripping. Unnecessary tripping may not be a major concern
for private docks and very small commercial or recreational facilities, but it could add insurmountable challenges
for medium and large commercial marinas where false tripping of circuit breakers would become a massive and
unmanageable nuisance.

The second point is related to how the code section 555.3 actually reads and related to the above. The 2014
code allows you to put ground fault protection at the branch breakers ONLY as an alternative which would likely
limit a false trip of the main circuit breaker. The 2017 code requires that ALL breakers should have ground fault
protection feeding any docking facilities which includes the main breaker.

Also did you know that all electrical equipment and wiring produce small amounts of leakage current. There is a
maximum allowable leakage current for hand-held, movable and stationary electrical appliances at about 3.5mA.
This is interesting and makes sense as this falls just below the 6mA people protection rating for devices. With
boating, leakage current studies were conducted and concluded at an average of 3.9mA of leakage current was
present on each vessel. (Even if everything was wired correctly!!)

So, picture this: you have a dock with 5 boats plugged into the pedestals along the dock each with 3.9mA which
totals to 19.5mA. This is less than the 30mA threshold and nothing should happen. However, a problem for the
main breaker is introduced if there is say 2 docks on separate branch circuits. Keeping the quantity of boats the
sameyou could potentially have 39mA of leakage current seen by the main breaker which causes the nuisance
trip.

So, it seems like we are getting better with ground fault trip thresholds however this is likely increasing the
amount of possible nuisance trips that could occur.

Some experts believe this section of the code will be re-written for the 2020 code cycle to perhaps add a time
delay threshold on the main breaker or possibly change it back to the 2014 code cycle which actually doesnt
require ground fault protection on the main. Or quite possibly allow the main breaker to have a 100mA threshold
with the branch circuits at 30mA.

Hopefully this article finds you well and can be used as a reference for your project needs.
If anyone would like to contribute to the Rochester Engineer magazine and add an article or
would like to request information on a specific topic (not limited to Electrical) just email me
at beliasz@bergmannpc.com. As always, any comments are appreciated! Thank you for
reading.

Brett Eliasz, P.E., LEED AP BD+C ,
RES Director

res - technical corner MAY 2020 The ROCHESTER ENGINEER | 7