when is your service maxed?

[syarn]

if an engineer says
"...The electrical panel is 400amp/240v/1 ph
We currently have 335 amps connected to the panel before the addition of the dishwasher
The dishwasher will overload the panel..."
the dishwasher looks to have 50 rated amps, 60 amp minimum supply circuit conductor ampacity & 60 amp maximum overcurrent protective device per the spec sheet.
when I add 50 amps to 335 amps I get 385 amps how does that over load the panel?

 

[augie47]

My guess is that it may have to do with the distribution of the loads. One phase is most likely loaded more than the other

 

[jxofaltrds]

if an engineer says
"...The electrical panel is 400amp/240v/1 ph
We currently have 335 amps connected to the panel before the addition of the dishwasher
The dishwasher will overload the panel..."
the dishwasher looks to have 50 rated amps, 60 amp minimum supply circuit conductor ampacity & 60 amp maximum overcurrent protective device per the spec sheet.
when I add 50 amps to 335 amps I get 385 amps how does that over load the panel?

It's like a checkbook you still have checks you still have money. Kidding.

Try this:

http://www.mikeholt.com/documents/calculations/formulas/ResidentialLoadCalculations.xls

 

[ptonsparky]

Actual current reading or just connected load?

 

[broadgage]

If 335 amps is the connected load, then it is PROBABLY fine, since it is most unlikely that all connected loads will draw full current at the same time. (how much of the 335 amps is 20 amp lighting circuits with only a few lamps ? or outlet circuits serving only a single low power appliance ?)

If 335 amps is the actual measured load, then adding another 50 amps is PROBABLY unwise, although 335 and 50 is clearly less than than 400, it is getting too close for comfort, remembering that the actual load at the time of measurement may not have been the maximum.
What if it is already 395 at times andyou add another 50 ?

Adding another 50 amps should be OK IF, AND ONLY IF you can be certain that the measured 335 was the maximum load, and not a "one off" snapshot, perhaps far below the actual maximum.

 

[T.M.Haja Sahib]

If 335A is the maximum demand (this you have to find out by consulting the utility or by other means such as by installing a maximum demand ammeter in the panel ), then adding 50A load is no problem.

 

[Strathead]

if an engineer says
"...The electrical panel is 400amp/240v/1 ph
We currently have 335 amps connected to the panel before the addition of the dishwasher
The dishwasher will overload the panel..."
the dishwasher looks to have 50 rated amps, 60 amp minimum supply circuit conductor ampacity & 60 amp maximum overcurrent protective device per the spec sheet.
when I add 50 amps to 335 amps I get 385 amps how does that over load the panel?

But you are asking two separate questions here. "if an engineer says..." if he is paid to provide a design and his license is on the line then the panel is overloaded as soon as he says it is. That is question one.

Question 2, the code has extensive examples and the internet is loaded with software to calculate loads for all different kinds of situations. Including the ability to use actual electrical usage data. It is overloaded per the NEC when these calculations are properly done and show an overload potential.

However, the panel is really overloaded when the breaker trips.

 

[ptonsparky]

But you are asking two separate questions here. "if an engineer says..." if he is paid to provide a design and his license is on the line then the panel is overloaded as soon as he says it is. That is question one.

Question 2, the code has extensive examples and the internet is loaded with software to calculate loads for all different kinds of situations. Including the ability to use actual electrical usage data. It is overloaded per the NEC when these calculations are properly done and show an overload potential.

However, the panel is really overloaded when the breaker trips.

I have seen fuses designed and made by engineers that they used in there own mfg plant. :jawdrop:

It never hurts to ask more questions.

 

[kingpb]

Based on the description: 400A/240V 1ph, there are no 120V loads, this is intended to feed 2-pole loads only and therfore both busses are carrying 335A, equally.

If that is all considered continuous load, then it is supposed to be only loaded to 320A, i.e. 80% of 400A.

In which case the 335A is already putting it over. You can add diversity factors, but that would have to be acceptable to the design engineer. It sounds like this is a kitchen? Which means during busy hours there may not be much diversity to apply.

Certainly using the logic above, adding the diswasher would cause the panel to be overloaded by definition.

 

[T.M.Haja Sahib]

.....In which case the 335A is already putting it over.

I think the panel may be rated for 100% loading and the design engineer concern was for any tripping due to added load during starting.

 

[jim dungar]

Many 120/240V 1-phase services are actully fed using 320A meter sockets.

 

[kingpb]

I think the panel may be rated for 100% loading and the design engineer concern was for any tripping due to added load during starting.

That is a lot of speculation, and unless somebody can tell me it's 100% rated, then it isn't. If this was an IEC/overseas job I would agree, but not in the US.

 

[petersonra]

It is overloaded if there is smoke coming out of the utility xfmr.

 

[jim dungar]

It is overloaded if there is smoke coming out of the utility xfmr.

In that case your service may be fine, it is the utility transformer that is overloaded.

 

[kenaslan]

Has a 30 day demand study been done as required by code? Are there both A/C and heating loads that will never be on at the same time? What kind of main?

Look on the bright side. Tell them the engineer said the panel is maxed. Then sell them a new panel, and make a bigger profit.

 

[petersonra]

Has a 30 day demand study been done as required by code? Are there both A/C and heating loads that will never be on at the same time? What kind of main?

Look on the bright side. Tell them the engineer said the panel is maxed. Then sell them a new panel, and make a bigger profit.

sometimes the simple answer is the best.

 

[kwired]

It is overloaded if there is smoke coming out of the utility xfmr.

In that case your service may be fine, it is the utility transformer that is overloaded.

correct. Don't expect POCO to provide a 400 amp transformer just because you have a 400 amp service, they only care about how much average load there is and have some other methods of determining peak demand and duration as well as how long of a cool down period there will be to help them decide when a larger transformer may be needed.

Assuming engineer did a careful enough study of what is there - it is probably time for some upgrading. Even if existing equipment will operate with the new added load- you are one step closer to the next added load being a problem. It really is more complex than just will it handle the added load, future considerations may help drive this decision.

 

[Smart $]

That is a lot of speculation, and unless somebody can tell me it's 100% rated, then it isn't. If this was an IEC/overseas job I would agree, but not in the US.

I agree (not included :happysad::huh:)...

However, "Article 230, VII. Service Equipment — Overcurrent Protection" does not require OCP to be equal or greater than "The sum of the noncontinuous loads plus 125 percent of continuous loads." Regarding services, only service-entrance conductors are subject to that requirement. The requirement for Service OCP is that it not exceed the ampacity of the connected service conductor... :huh: Then that requirement is shot to heck under the exception for two to six service disconnecting means.

 

[T.M.Haja Sahib]

That is a lot of speculation, and unless somebody can tell me it's 100% rated, then it isn't. If this was an IEC/overseas job I would agree, but not in the US.

Many 120/240V 1-phase services are actully fed using 320A meter sockets.

If such is the case, the OP not only has to change the panel, but also change the service either to 120/208V single phase or to enhance to 120/240V three phase.

 

[kwired]

That is a lot of speculation, and unless somebody can tell me it's 100% rated, then it isn't. If this was an IEC/overseas job I would agree, but not in the US.

We don't know if the determination of being loaded in the OP included 125% for continuous loads or not.

If you are calculating load according to art 220 and come up with less than 400 amps then a 400 amp supply should be sufficient. We also do not know if we can apply demand factors to the load that is being added, since we don't know much about what other loads may be present.