feeder calculation, Would you sweat it?

[brother]

Just saw another job they did with a feeder calculation for kitchen equipment. Very similar to the one I posted about before, here is the calculation

17a 208v = 3536
16a 208v= 3328
(espresso)5200watt
2 900va coffee grinders= 1800va
water heater 2000watts
2 duplex receptacles= 360va
total 15864 va
15864 X .65= 10311.6

10311.6 + 360=10670.6

10670.6/208= 51.4 amps

They used a 50amp breaker/circuit for this run.

Would you sweat the 1.4 amp since technically the circuit is too small for the run?

 

[augie47]

Do you know what size/type conductor was used ?
(I ask as it may be possible to use a larger OCP)

 

[kwired]

Just saw another job they did with a feeder calculation for kitchen equipment. Very similar to the one I posted about before, here is the calculation

17a 208v = 3536
16a 208v= 3328
(espresso)5200watt
2 900va coffee grinders= 1800va
water heater 2000watts
2 duplex receptacles= 360va
total 15864 va
15864 X .65= 10311.6

10311.6 + 360=10670.6

10670.6/208= 51.4 amps

They used a 50amp breaker/circuit for this run.

Would you sweat the 1.4 amp since technically the circuit is too small for the run?

Though the NEC tells us how to size this, IMO it is more of a design issue and as long as proper overcurrent protection is provided for the conductors I wouldn't even bother looking at this if I were an inspector. That said to keep me from looking like a fool later when it potentially is overloaded I would have run at least a 60 amp feeder for this, and am even more likely to run a 100 amp feeder just in case they decide to add something later.

 

[brother]

Do you know what size/type conductor was used ?
(I ask as it may be possible to use a larger OCP)

They used a #8 copper. #8 only good for 50amps and the calculation is 51. Also this is a long run (about 100ft), they didnt even account for a voltage drop. Even though its not required per NEC, it is strongly recommended.

 

[augie47]

From my read, the feeder is required to have an ampacity equal to or greater than the calculated load {see 215.2(A)(1)}. Since the 220.56 calculations already have a diversity factor, as an inspector I would not hesitate to reject the install you presented.

 

[cadpoint]

*I can see the unaccounted factor on lack of receptacles, OK, they always need more than
they think they might want, know, or the oh yeah factor. EX. small refrigator for milk and or public cold drink sales.

Your water heater imply's a six gallon water heater, or it's based of a house unit or visa versa, which would make accounting for it incorrect, it's techanically a smaller pre-wattage. Just be careful not to use a residental number in a commerical setting. It needs to make it past a health inspection in the end, EX. required water flow rates in kitchens is different.

I realize you need to price this, just don't let them embrass you!*

 

[brother]

*I can see the unaccounted factor on lack of receptacles, OK, they always need more than
they think they might want, know, or the oh yeah factor. EX. small refrigator for milk and or public cold drink sales.

Your water heater imply's a six gallon water heater, or it's based of a house unit or visa versa, which would make accounting for it incorrect, it's techanically a smaller pre-wattage. Just be careful not to use a residental number in a commerical setting. It needs to make it past a health inspection in the end, EX. required water flow rates in kitchens is different.

I realize you need to price this, just don't let them embrass you!*

Im not 'bidding' this job. This is a project that was done by others. I was looking at the work and was wondering should I say something about the load. whether I should 'sweat it' or not.

 

[Smart $]

A few 208V loads are mentioned and have to assume some are 120V. Is this 120/208V 1? 3W? ...or 208/120V 3? 4W and errantly calculated as 1??

If 1?, may be able to squeeze out that extra 1.4A or more using a vector-based calculation. Not provided for in Article 220, but not specifically prohibited either.

 

[brother]

A few 208V loads are mentioned and have to assume some are 120V. Is this 120/208V 1? 3W? ...or 208/120V 3? 4W and errantly calculated as 1??

If 1?, may be able to squeeze out that extra 1.4A or more using a vector-based calculation. Not provided for in Article 220, but not specifically prohibited either.

This is single phase 3W. In laymans terms, 2 hots 1 neutral

 

[Smart $]

This is single phase 3W. In laymans terms, 2 hots 1 neutral

Got it...

To do a vector-based calculation, would need to distinguish which are 208V and which are 120V...but I'm fairly certain it would reduce the load by 1.4A or more.

 

[brother]

Got it...

To do a vector-based calculation, would need to distinguish which are 208V and which are 120V...but I'm fairly certain it would reduce the load by 1.4A or more.

How would this comply with the NEC as augie47 had quoted?

 

[kwired]

How would this comply with the NEC as augie47 had quoted?

To start with total VA was divided by 208 to come up with the amps in the OP.

Reality is some of those loads are not 208 volt loads so that figure is not entirely accurate, but in many cases is close enough . To make up the apparent overload of only 1.4 amps by coming up with an accurate value is going to be pretty likely.

Now if the applied voltage were 120/240 and the 120 volt loads are balanced then the method of dividing the total VA by 240 would be accurate.

Example:

two 1200VA loads @ 120 volts, that is 10 amps each load, put one on phase A, one on phase B and connect neutral to each and they both still draw 10 amps.

one 1200VA 208 volt load is 5.7 amps though.

Now put one previously mentioned 120 volt load on phase A and one on phase B of a 208/120source and do not connect the neutral to the source - you only apply 208 volts and will have reduced total VA (on a resistive load). Do the same with a 240 volt source and output is still 120 across each component and still a total of 1200 VA.

 

[Smart $]

How would this comply with the NEC as augie47 had quoted?

An Article 220 calculation is simple arithmetic addition of volt-amperes based on a simplified AC electric model. With part-wye single-phase systems, the line-to-line currents of a similarly simplified model are not in phase with the line-to-neutral currents. They do not add arithmetically. Instead, vector math must be used to determine combined currents, often resulting in lower line current than using the arithmetic model.

 

[stew]

I would not have used a 50 amp circuit for this. 51.4 = a 60 amp circuit IMHO. WWhat's done is done however and will probably work just fine. If I were the inspector and had the load calc. I would reject it.?