When should you ask utility if there is enough power available?

[kwired]

If I do an installation, I am obliged to do a load calc to determine if the service equipment is not overloaded.

But if I determine that the service equipment is correctly sized per article 220, at what point do I need to say anything to the POCO? Remember that the POCO has their own rules, and their installation is often undersized compared to the service equipment.

-Jon

For a start you maybe compare your load with transformer. Especially if there is higher levels of continuous loads involved.

When I am doing grain storage sites, other than commercial elevators, I mostly ignore loading and unloading equipment. The aeration fans are generally the major load, and on top of that when they run they often run 24/7 for days at a time. Loading/unloading equipment only runs 10-15 minutes at a time then may sit several hours before running again.

Bottom line is you kind of need to know the loading situation. Industrial plant - production loads may be fairly continuous, or they may be higher during one phase of operations than during others. Total connected load and what all runs at same time and for how long can be widely different.

 

[AC\DC]

The engineer for are POCO said even if you add a small 1/2 hp motor. Submit a load calculation sheet and then it throws the burden on them, in case something happens down the road.

 

[don_resqcapt19]

No engineer I know has ever done a calculation to check if load is adequate, they just simply did estimations

You are required to use one of the methods spelled out in 220.87 where adding additional load to an existing service. An "estimate" is not one of the permitted methods.

 

[Tainted]

You are required to use one of the methods spelled out in 220.87 where adding additional load to an existing service. An "estimate" is not one of the permitted methods.

So if I add a receptacle for a 1/30HP condensate pump to a 200 story building(over exaggerating), I would need to go through all the trouble of calculating the load of the entire building or do 220.87? That’s nuts. I don’t care what the code is, I’m not gonna explain the client to this and look like an idiot

 

[petersonra]

So if I add a receptacle for a 1/30HP condensate pump to a 200 story building(over exaggerating), I would need to go through all the trouble of calculating the load of the entire building or do 220.87? That’s nuts. I don’t care what the code is, I’m not gonna explain the client to this and look like an idiot

You don't have to do the whole calculation over. Just update the old one to include the new load(s).

 

[Tainted]

You don't have to do the whole calculation over. Just update the old one to include the new load(s).

There’s no records of the old calculations, I work on old ancient buildings

 

[petersonra]

There’s no records of the old calculations, I work on old ancient buildings

If that is the case how would anyone know whether a new load could be accomodated?

I am inclined to agree that having to do a new load calculation for an old system is a pain in the neck just to add a small load, and I personally would not get real uptight about doing so, or not. But, the AHJ would be well within its authority to ask for it when you apply for the permit to do the work.

By the way, if there is no load calculation, that suggests there might be other necessary information missing. How would you know what the SCCR of the equipment would need to be? Or what the AIC rating of the new OCPD has to be?

 

[Tainted]

If that is the case how would anyone know whether a new load could be accomodated?

I am inclined to agree that having to do a new load calculation for an old system is a pain in the neck just to add a small load, and I personally would not get real uptight about doing so, or not. But, the AHJ would be well within its authority to ask for it when you apply for the permit to do the work.

By the way, if there is no load calculation, that suggests there might be other necessary information missing. How would you know what the SCCR of the equipment would need to be? Or what the AIC rating of the new OCPD has to be?

If you have a lot of experience, a lot of this can be done using the rule of thumb. But obviously that’s not acceptable by code

 

[petersonra]

If you have a lot of experience, a lot of this can be done using the rule of thumb. But obviously that’s not acceptable by code

what "rule of thumb" would tell you the required SCCR or AIC required?

 

[Tainted]

what "rule of thumb" would tell you the required SCCR or AIC required?

Depends the conditions, it’s called “rule of thumb” for a reason…

 

[petersonra]

Depends the conditions, it’s called “rule of thumb” for a reason…

I don't see any case where a "rule of thumb" could determine either SCCR or AIC.

 

[Tainted]

I don't see any case where a "rule of thumb" could determine either SCCR or AIC.

Its all about experience

 

[petersonra]

Its all about experience

no. it is about what the required SCCR or AIC is. Neither can typically be determined by any "rule of thumb" or experience.

 

[electrofelon]

no. it is about what the required SCCR or AIC is. Neither can typically be determined by any "rule of thumb" or experience.

I'm Gunna sorta disagree. I have a pretty good idea of approximate impedance values and transformer sizes and conductor impedance, so sometimes I can look at a setup and know whether I have an issue or not. Obviously if it's UG and you can't see any of the power company's stuff it's a different story.

 

[petersonra]

I'm Gunna sorta disagree. I have a pretty good idea of approximate impedance values and transformer sizes and conductor impedance, so sometimes I can look at a setup and know whether I have an issue or not. Obviously if it's UG and you can't see any of the power company's stuff it's a different story.

What you are describing is a calculation, not a rule of thumb.

 

[electrofelon]

What you are describing is a calculation, not a rule of thumb.

Not sure that "that service drop looks pretty long, I think we're fine with 22k" is a calculation....

 

[petersonra]

Not sure that "that service drop looks pretty long, I think we're fine with 22k" is a calculation....

Does the AHJ accept that type of answer when you go to get a permit?

 

[gadfly56]

Depends the conditions, it’s called “rule of thumb” for a reason…

And if things go sideways...

I can see the conference room now, during deposition:

<Plaintiff's counsel> "So, Mr. Tainted, let's discuss the load calculations you performed for this installation..."

 

[Charged]

Personally I don’t think it’s clear if the OP is regarding the load on the customer service equipment or the utility transformer. If it’s not about the service equipment and he just wants to tell the utility about the additional load then I don’t think he needs the full NEC calc. What his scope entails regarding the customer equipment may require a NEC load calc for the the electrical permit. Looks like a pretty easy case to use 12 month demand from the utility bills and add the new load.

 

[Tainted]

Not sure that "that service drop looks pretty long, I think we're fine with 22k" is a calculation....

I do the same thing! Recently done it with a long feeder about 150’ long