100 amp Breaker tripping, 75 amp water heater?

tankless water heater — Mon, 12 Dec 2011 06:30:09 +0000

Hi – I have one of these on a dedicated line (old central heater unit) which now serves a 75 amp tankless water water heater and nothing else. 6 gauge wire. It is tripping after about 5 minutes running at 57-60 amps according to my clamp meter. But it has pulled more amps than that without tripping so it seems to be a time function. Breaker gets quite hot at the terminal screw end. Does this sound like a worn-out breaker or some other problem? Thank you if you have time to reply, Jeff
Thank you for the replies. I was guessing at the wire gauge from online pics, the wire is from an old installation, over 20 years old. The wire is 7 strands (about 12 ga ea) and with insulation measures 3/8 inch in diameter which puts it between 2 and 4 gauge per an online source I have since found.

The wire is Building Wire- Type THW PVC Insulation, 600V from some faint stampings on the insulation.

It originally powered an attic furnace and blower.
Power runs direct into a 100 amp cutoff beneath the meter and gives no other service.
We are rural so a quick jaunt to the hardware store is impractical today to verify size.

The tankless heater is brand new and per their spec requirements: Required the installation of “one circuit of 80 amps or 1 circuits of 60 amp and # 6 wire”. (their language) which is confusing to me.

Please note the clamp meter gave me amp reading ranges from <40 amps to >85 amps as the unit’ build-in circuit breakers monitored the current. The 100 amp break
LOOKS LIKE ALL MY ADDITIONAL DETAILS DIDN’T POST:

The 100 amp breaker tripped while showing a reading of 57 – 60 amp currents.

I have not yet removed the breaker from the box, by the time I got to that point, the temp outside at the box was near 105, and i was getting a bit weary.

Choices:

1. Replace with a 75 amp breaker if there is one to fit

2 Replace the entire cut-off box and breaker with another brand.

Note this does not run through my 100 amp household service which is served by smaller gauge wire and runs 3 window units, microwave, stove/oven and TV/Computers with no problems in 16 years.

Thank you for your patience with my question, and I do have a thick skin (grin) Jeff

(Run is about 70 feet, I disconnected from the obsolete attic unit and ran under the house, there may be 10′ of excess length which could be cut.”
The questionable breaker is a FEDERAL PACIFIC Stab-Lok FPE 2P 100 Amp Type NA BREAKER,
I found a new one online for about $250 which sounds ridiculous, used in the $35-$90 range.

I also found several less-than-complimentary reviews of these FP breakers.

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100 amp Breaker tripping, 75 amp water heater?