80% rule

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Poccur

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Location
Virginia
Apologies if this has been done to death before but I am working an issue with the 80% rule as it applies to portable generators...

I have a 60kW diesel gen with a couple of 100amp outputs. My electrical 'go to guy' is saying that according to NEC the breaker for the 100amp connector needs to be 125amp because of the 80% rule if I need 100amps continuous. I feel that a 100amp breaker and a 100amp conductor and a 100amp connector can be expected to run at 80amps continuous. If I need 100amps continuous then I need to upsize everything, the connector and conductor go to 200amp, I can use a 125amp breaker and now the system is sized to run 100amps continuous.
He wants to upsize breaker to 125amps but leave IEC60309 connector at 100amps and not change conductor.
I think this is pushing it, so far as I know IEC connectors are only tested to 110% so you could be pulling 120amps and be 10amps the other side of the connector rating and probably way outside of the existing conductor..
Am I reading it wrong?
Thanks
 
petersonra

petersonra

Senior Member
Location
Northern illinois
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engineer
There really is not an "80%" rule. There is a rule that the breaker can either be a standard breaker rated at 80% if you have a 100 A non-continuous load or a 100% rated breaker if you have a 100% continuous load. Do you need 100 Amps continuous? What is connected to the outlet?

The connector is not affected by this requirement. However, if it is an IEC connector it may not be UL listed and thus you could not use it anyway.

The conductor sizing is not affected by this situation either, however as a practical matter the numbers calculated for the conductors might come out to more than 100% of FLC. What did your load calculation for this circuit come up to?
 
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Poccur

Member
Location
Virginia
I need 100amp continuous at 208V three phase..so my thought was to upsize the conductor, breaker and connector to handle 125amps...the next size up in IEC series 2 is 200amp...
The problem i have is over sizing the breaker but leaving the conductor and the connector the lower size..if you want 100amps continuous you have to go to a larger conductor and a larger connector...
A 100amps IEC 60309 connector is tested to 110 amps, if you put a 125amps breaker on it then you are in untested territory from 110 amps to 125 amps...All I am saying is if you want 100amps continuous then you have to upsize the breaker AND the conductor and connector...
 
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Poccur

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Location
Virginia
The issue is my generator guy is saying just changing the breaker only to 125amps is enough for the circuit to carry 100amps continuous...He is not changing the conductor size or the connector...
 
petersonra

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Poccur said:
The issue is my generator guy is saying just changing the breaker only to 125amps is enough for the circuit to carry 100amps continuous...He is not changing the conductor size or the connector...
Click to expand...
I don't see why the connector would need to be changed, unless the wire size got too big.
 
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Poccur

Member
Location
Virginia
It is an IEC 60309 connector, 100amp...My understanding is they are tested to 110% of rated...With a 125amp breaker on a 100amp connector then you can exceed 110amps before tripping and be outside the test range of the connector...
 
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