Adding Load to Existing Service

[hbendillo]

I am working on a project where in an existing restaurant, they want to renovate a large storage space to a micro brewery. So, we want to take off an existing panelboard to feed the brewery. This panelboard is the only viable option from which to feed the brewery. Will only bore you with the details of how the service to this restaurant is configured if you really want to know. But this panelboard is not individually metered so there is no long term record of the actual load on this panelboard. So, I had them install a meter to record over five days to get some idea of what we have. Bottom line, the highest average on any one leg of this three-phase circuit is 58 amps; Max amps is 88.97. Circuit for the panel: 175 amp circuit breaker, 480 volt, three-phase.

Using NEC demand factors, the load for the brewery is 219 amps at 208-volt, three-phase which translates to about 95 amps at 480 volts. Total with new load is 152.9 amps on our 480-volt panelboard. Assuming the 175 amp breaker is standard 80% rated the continuous load rating is 140 amps. So we have a problem.

Now, I am pretty confident that the actual demand for this brewery is significantly lower. But thanks to the NEC I can't test that evaluation. And even if it would, recording for five days just isn't enough data to make such a decision.

I don't see any recourse other than upgrading the service to this panelboard. The feeder for this panelboard could be up to 300 feet from the main service panel which located in an electrical room that is a part of this mall property. I guess I am just searching for alternatives. I know the owner is not going to want to pay the additional cost to upgrade the feeder.

 

[JDBrown]

Okay, let's back up a second. First off, as you probably know, 220.87(1) Exception requires you to use the maximum demand over a 30-day period if you don't have the maximum demand for one year available. But I understand that your 5-day test was just to see if there was any possibility of making this work.

The relevant portion of the language in that Exception is: "... the calculated load shall be permitted to be based on the maximum demand (measure of average power demand over a 15-minute period) continuously recorded over a minimum 30-day period ..."

With this in mind, I'm not entirely sure what you mean by "the highest average on any one leg of this three-phase circuit is 58 amps; Max amps is 88.97." Does this mean that 58 amps is the average over the 5 day period and 88.97 amps is the peak during that period? If so, then you'll need to use 88.97 amps in your calculation. Or did you mean that 58 amps is the highest average over any 15-minute period and 88.97 amps is the instantaneous maximum? In that case, you can use 58 amps in your calculation.

Once you have determined which is the appropriate number to use in the calculation, you have to add 25% to it per 220.87(2).

If we assume that you have to use 88.97 amps for your calculation, then 88.97A x 125% = 111 amps @ 480V, 3P. Now add your calculated load, and we get 111A + 95A = 206 amps @ 480V, 3P. This obviously won't work with your 175A breaker. In this case, you probably don't have any other options besides upgrading the feeder. You could, of course, search high and low for any demand factors you might be able to take, but I don't think shedding 31 amps via demand factors is very realistic here.

Now if, on the other hand, you are able to use 58 amps in the calculation, we come up with (58A x 125%) + 95A = 168 amps. This will work for you, based on 220.87(2) and (3):

(2) The maximum demand at 125 percent plus the new load does not exceed the ampacity of the feeder or rating of the service.
(3) The feeder has overcurrent protection in accordance with 240.4, and the service has overload protection in accordance with 230.90.

Of course, you're still not in the clear in this case, as your load test has to last 30 days, not five, but at least you can see it might be worth it to move forward with the 30-day test.

Really, though, everything hinges on exactly what your two numbers (58 amps and 88.97 amps) actually are.

 

[hbendillo]

Thanks for you reply. In your second scenario, where you used the 58 amp load assuming it was the legitimate 15 minute average demand, will the 168 amp estimated load work on a 175 amp circuit breaker considering that 80% of the circuit breaker's rating it is only 140 amps which is generally the continuous rating. I am assuming it is a typical 80% rated breaker.

Thanks.

 

[hbendillo]

Thanks for you reply. In your second scenario, where you used the 58 amp load assuming it was the legitimate 15 minute average demand, will the 168 amp estimated load work on a 175 amp circuit breaker considering that 80% of the circuit breaker's rating it is only 140 amps which is generally the continuous rating. I am assuming it is a typical 80% rated breaker.

Thanks.

I'm sorry, I don't know why I get confused with the 80% rating versus the demand but we've already accounted for the continuous load by applying the 125% demand factor so our circuit breaker is good for the 168 amps you calculated using the 58 amp existing continuous load.

 

[SparkyHC]

no such thing...

no such thing...

would it help if there was no such thing as a 80% circuit breaker?

 

[hbendillo]

It would probably help if I described things better using the proper terminology.

 

[kingpb]

would it help if there was no such thing as a 80% circuit breaker?

There isn't such a thing. All breakers can carry 100% of their rating. It is how you use them, or where they are installed that causes them to be derated.

 

[hbendillo]

There isn't such a thing. All breakers can carry 100% of their rating. It is how you use them, or where they are installed that causes them to be derated.

Well yeah, technically no such thing. But all breakers cannot carry 100% of their rating continuously. That is the point if I am not mistaken.

 

[JDBrown]

A standard breaker can be loaded up to 100% of the noncontinuous load + 125% of the continuous load. These are often erroneously referred to as "80% rated breakers."

So-called "100% rated breakers" are listed for continuous loading at their marked rating, and can be loaded up to 100% of the noncontinuous load + 100% of the continuous load.

As long as your 95 Amps @ 480 volts included the required 125% for continuous loads, you should be okay with a standard breaker, assuming the 58 amp load was the legitimate 15 minute average demand over not less than 30 days.

 

[curt swartz]

If the load existing feeder is so small why would you use a recorder? Find all the equipment connected and do the proper calc.

How do you know the existing service can handle the additional loads? Just because there is a 175 amp feeder running to this unit doesn't mean the clac's for the service included the full 175 amps.

 

[JDBrown]

If the load existing feeder is so small why would you use a recorder? Find all the equipment connected and do the proper calc.

Excellent point. I thought I had mentioned that earlier, but looking back I didn't. I must have been thinking of another thread. Thanks for bringing it up here. I was acting on the assumption that if the OP was able to determine the existing loads, he wouldn't have bothered with the load test, but I guess that isn't necessarily the case.

How do you know the existing service can handle the additional loads? Just because there is a 175 amp feeder running to this unit doesn't mean the clac's for the service included the full 175 amps.

Another excellent point. I've been focusing on helping the OP with the issues he's having with the panelboard he wants to feed the microbrewery from, but you're right; he has to make sure he's not overloading anything, all the way back to the service.

To hbendillo:
Remember that if you're doing a load test on this panel, you may have to do the same on every panel that feeds it going all the way back to the service. This can be costly and time consuming, but if you don't have load information on any of the panels in your distribution system it's what you have to do in order to justify the added load.

 

[kingpb]

Breakers, all types, can carry the rated current continuously. The rating is based on certain temperatures and methods of installation.

I have attached a time current curve for a 40A breaker. It clearly shows that it can carry 40A continuously.

The fact the NEC only allows loading a breaker to 80% of its continuous rating, unless specifically 100% rated, is because of the method in which it is installed.

 

[iwire]

Breakers, all types, can carry the rated current continuously. The rating is based on certain temperatures and methods of installation.

I have attached a time current curve for a 40A breaker. It clearly shows that it can carry 40A continuously.

The fact the NEC only allows loading a breaker to 80% of its continuous rating, unless specifically 100% rated, is because of the method in which it is installed.

View attachment 9013

And the point of this is what?

The fact is neither UL or the NEC will let us use the breaker at 100% continuously.

 

[__dan]

Breakers, all types, can carry the rated current continuously. The rating is based on certain temperatures and methods of installation.

I have attached a time current curve for a 40A breaker. It clearly shows that it can carry 40A continuously.

The fact the NEC only allows loading a breaker to 80% of its continuous rating, unless specifically 100% rated, is because of the method in which it is installed.

View attachment 9013

I've asked the factory engineer if I would get nuisance tripping loading a 100% continuous rated breaker at 100%. The application was a 1 MVA load bank for generator testing, and that's what the drawing showed, the breaker loaded at 100%. The breaker manufacturer's engineer said "it would not trip but they would not guarantee it".

 

[kingpb]

And the point of this is what?

The fact is neither UL or the NEC will let us use the breaker at 100% continuously.

Au contraire, mon fr?re, simply utilize the breaker under the same conditions it was tested.

Not to put words in your mouth, but I am thinking you meant to say under conditions typically encountered, which I concur with your logic, it will probably not be able to be utilized at its 100% rating. However, it is erroneous to make a blanket statement that UL or NEC will not allow it. Especially since UL did approve the 100% rating; albeit under certain conditions.

Cheers~

 

[hbendillo]

A standard breaker can be loaded up to 100% of the noncontinuous load + 125% of the continuous load. These are often erroneously referred to as "80% rated breakers."

So-called "100% rated breakers" are listed for continuous loading at their marked rating, and can be loaded up to 100% of the noncontinuous load + 100% of the continuous load.

As long as your 95 Amps @ 480 volts included the required 125% for continuous loads, you should be okay with a standard breaker, assuming the 58 amp load was the legitimate 15 minute average demand over not less than 30 days.

Agreed. Thanks for your help.

 

[hbendillo]

Excellent point. I thought I had mentioned that earlier, but looking back I didn't. I must have been thinking of another thread. Thanks for bringing it up here. I was acting on the assumption that if the OP was able to determine the existing loads, he wouldn't have bothered with the load test, but I guess that isn't necessarily the case.


Another excellent point. I've been focusing on helping the OP with the issues he's having with the panelboard he wants to feed the microbrewery from, but you're right; he has to make sure he's not overloading anything, all the way back to the service.

To hbendillo:
Remember that if you're doing a load test on this panel, you may have to do the same on every panel that feeds it going all the way back to the service. This can be costly and time consuming, but if you don't have load information on any of the panels in your distribution system it's what you have to do in order to justify the added load.

Thanks to you both. I am connecting the service for brewery ahead of all other panelboards associated with this feeder which originates at the main service panel. I have a load profile from the power company for the main service panel. There is zero documentation to work with for the restaurant so I cannot recreate it without a lot of work. So I think legitimately measuring the load for the feeder in question is my only option.

 

[hbendillo]

Excellent point. I thought I had mentioned that earlier, but looking back I didn't. I must have been thinking of another thread. Thanks for bringing it up here. I was acting on the assumption that if the OP was able to determine the existing loads, he wouldn't have bothered with the load test, but I guess that isn't necessarily the case.


Another excellent point. I've been focusing on helping the OP with the issues he's having with the panelboard he wants to feed the microbrewery from, but you're right; he has to make sure he's not overloading anything, all the way back to the service.

To hbendillo:
Remember that if you're doing a load test on this panel, you may have to do the same on every panel that feeds it going all the way back to the service. This can be costly and time consuming, but if you don't have load information on any of the panels in your distribution system it's what you have to do in order to justify the added load.

If the load existing feeder is so small why would you use a recorder? Find all the equipment connected and do the proper calc.

How do you know the existing service can handle the additional loads? Just because there is a 175 amp feeder running to this unit doesn't mean the clac's for the service included the full 175 amps.

There are four panelboards associated with this feeder, zero documentation and incomplete and inaccurate panelboard directories.