6 handle rule question

[sokbok]

Can the cumulative ampacity of the 6 service disconnects allowed by 230.71 be greater then the rating of the CT cabinet?
Thanks

 

[Jraef]

Unrelated issues. The 6 hand rule has no correlation to service size and vice-versa.

But also, the cumulative value of circuit breakers has little to no relationship to the service size, other than no breaker on the service can be larger than the service capacity. So for example if you have a 200A service, you can have a 6 separate 200A service breakers on it, but you cannot exceed 200A in actual load. So you cannot have a 300A service breaker on that service drop.

 

[don_resqcapt19]

I don't think that the code directly addresses this question.
I think I would say it is ok based on Exception #3 to 230.90(A), however that only addresses service conductors and not equipment.

 

[Buck Parrish]

Can the cumulative ampacity of the 6 service disconnects allowed by 230.71 be greater then the rating of the CT cabinet?
Thanks

Yes, you go by the calculated load.

 

[jaggedben]

I don't think that the code directly addresses this question.
I think I would say it is ok based on Exception #3 to 230.90(A), however that only addresses service conductors and not equipment.

The CT cabinet busses are service conductors. That is totally the right code section for this question.

 

[jaggedben]

... So for example if you have a 200A service, you can have a 6 separate 200A service breakers on it, but you cannot exceed 200A in actual load. So you cannot have a 300A service breaker on that service drop.

The aforementioned exception doesn't actually say that. Although I agree that it should raise an eyebrow and prompt extra scrutiny.

 

[sokbok]

Great discussion. NEC2023 230.9(A) exception #3:

Exception No. 3:
Two to six circuit breakers or sets of fuses shall be permitted as the overcurrent device to provide the overload protection. The sum of the ratings of the circuit breakers or fuses shall be permitted to exceed the ampacity of the service conductors, provided the calculated load does not exceed the ampacity of the service conductors.

So this phrase "calculated load" is critical. What is confusing is the utility will sometimes put conductors that I feel to be way undersized from their transformer to the CT cabinet and its concerning, but they can monitor usage and adjust if necessary I guess.
Having the cumulative ampacity of say (5) 200Amp disconnects connected to a CT cabinet that is rated for 600amps, intuitively does not make sense for obvious reasons. 1000amps of possible load on 600Amp cabinet....but the code allows it using this one phrase "calculated load" which is concerning because that load can change over time and the service will not always be re-evaluated. the 6 handle thing is helpful, but weird.
Its also hard to divide off a CT cabinet unless it has many lugs.

 

[ggunn]

So this phrase "calculated load" is critical.

I'm likely going to open a can of worms here, but isn't a "calculated load" a bit of a guess?

 

[kwired]

If you have an 800 amp main and six 200 amp feeders that never trips anything you should easily been able to have six 200 amp mains with 800 amp supply conductors.

 

[jaggedben]

I'm likely going to open a can of worms here, but isn't a "calculated load" a bit of a guess?

No, it's proscribed in Article 220.

 

[jaggedben]

...

So this phrase "calculated load" is critical. What is confusing is the utility will sometimes put conductors that I feel to be way undersized from their transformer to the CT cabinet and its concerning, but they can monitor usage and adjust if necessary I guess.
...

Where they own the wires they operate under a completely different set of rules. (NESC) Don't let it confuse you.

 

[jaggedben]

..


Having the cumulative ampacity of say (5) 200Amp disconnects connected to a CT cabinet that is rated for 600amps, intuitively does not make sense for obvious reasons. 1000amps of possible load on 600Amp cabinet....but the code allows it using this one phrase "calculated load" which is concerning because that load can change over time and the service will not always be re-evaluated. the 6 handle thing is helpful, but weird.
...

To your point about services changing, often the load actually goes down (de-industrializing, efficient lighting conversions) when facilities are repurposed. And very, very often feeders are way oversized for the calculated load anyway. So it's not inconceivable in the least for funky situations to arise. For example a former industrial facility is coverted to offices and needs new HVAC, and the HVAC would overload either of the (2) existing 200A discos, so it gets added as a third disco, but the light and plug load on the reused existing discos is, like, only 150A. So something like 600A of discos on a 400A service where calculated load is less than 350A.

 

[ggunn]

No, it's proscribed in Article 220.

proscribed: forbidden, especially by law; denounced or condemned

Is that what you meant to say?

 

[jaggedben]

Meant prescribed. Sorry.

 

[ggunn]

Meant prescribed. Sorry.

That's kinda what I thought, but in here you never know.

I have looked at Article 220, but it looks like educated guessing to me.

 

[jaggedben]

I have looked at Article 220, but it looks like educated guessing to me.

Well, a person following the rules does not have to guess, they just follow the rules. But regarding the people who made the rules I see your point. It's not only guessing, but probably overestimating 99% of the time.

 

[wwhitney]

But regarding the people who made the rules I see your point. It's not only guessing, but probably overestimating 99% of the time.

So then we can call it a very conservative guess, meaning that in an NEC compliant installation without defects, the incidence of service conductors burning up without any of the service OCPD tripping should be very low.

Cheers, Wayne

 

[xformer]

If you have an 800 amp main and six 200 amp feeders that never trips anything you should easily been able to have six 200 amp mains with 800 amp supply conductors.

I believe this only applies to Services. When installing a SDS this is not allowed.

 

[kwired]

To your point about services changing, often the load actually goes down (de-industrializing, efficient lighting conversions) when facilities are repurposed. And very, very often feeders are way oversized for the calculated load anyway. So it's not inconceivable in the least for funky situations to arise. For example a former industrial facility is coverted to offices and needs new HVAC, and the HVAC would overload either of the (2) existing 200A discos, so it gets added as a third disco, but the light and plug load on the reused existing discos is, like, only 150A. So something like 600A of discos on a 400A service where calculated load is less than 350A.

Different industrial operation does come in sometimes though and just might have more load demand than what was there before.

Former retail gets converted to restaurant - former retail only had HVAC and lighting for the most part, the restaurant has all this refrigeration and cooking equipment.

 

[JoeStillman]

I have looked at Article 220, but it looks like educated guessing to me.

You're all wrong - it's Voodoo!