Service Tap

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roc1

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What is code reqiurment on this application.We have a 2000 Amp 3 phase Service with 5-500mcm per phase.My question is this we are installing a 3 phase lighting panel wye with a 200 amp main breaker.What does the code say about tying directly to top of main service instead of MCC bucket for the lighting panel?The reason is this main service is buried already and we want the lighting panel to be on when power is off for lights in building.
Thanks
roc1
 
Hello Roc1 and welcome to the forum.

You wrote:
"The reason is this main service is buried already and we want the lighting panel to be on when power is off for lights in building. "


What does this mean?
Is the service already to capacity?
Buried... in what way?
 
Service Tap

Thanks for reply.Service is in Schedule 40 PVC.No it is not loaded we were going to add bucket in MCC for it anyway,but now we went ahead and installed its own conduit to pad mount transformer so it is good.I was wondering in future the same scenario could you just tie on top side of service if it was allowed for in load calculations.The reason is like I said to keep lights hot when power is off in off season.
 
roc
We have a 2000 Amp 3 phase Service with 5-500mcm per phase.
Click to expand...

A side note: Using 240.4(C), you have a possible code violation.
Ampacity of 5 #500 kcm = 5 x 380 = 1900 amps.
 
You are right.You can use the 90 C which is 430 x5 =2150Amps but you can only load it to the 75 C chart which is 1900Amp.All loads are continous which is 1600 Amps full load which is under 1900.
roc1
 
Service Taps

Service Taps

We kill main during offseason for power company demand charges this is in rural West Texas.Another problem is if you lost a bucket in the night and needed to turn Mains off you would have no lights or Single Phase power.I just wondered is it legal to tap off main service or is required to run to transformer like we did?
Thanks
roc1
 
You are right.You can use the 90 C which is 430 x5 =2150Amps but you can only load it to the 75 C chart which is 1900Amp.All loads are continous which is 1600 Amps full load which is under 1900.
Click to expand...

You can use the 90C rating only for temperature adjustments and derating
for more that 3 conductors in conduit and maybe some other conditions.
The 90C rating is not applicable in this installation. 240.4(C) does not allow rounding up to the next size OC device. The ampacity of the conductor must match the OC device rating when the OC device rating is over 800 amps. In this case the 1900 amps conductor is close but does not match the 2000 amp breaker.
 
There's one crucial piece of information missing here - Is this a main lug or main breaker service ? If it is a main lug, then you don't have a violation, you just have a 1900 amp service - not a 2000 amp service. If it is a main breaker, then you do have a code problem as indicated.

To answer the original question, if, in fact, it is a main lug panel AND you have open lugs on the main, you could tap a panel there and it would fall under the tap rules of 240 provided there are no more than 6 motions of the hand required to kill service to the building (your new panel included). If it is a main breaker service, you can not tap said panel ahead of the main.

I suspect it is a main breaker of some sort, but just wasn't clear.
 
Service Tap

Yes the Lighting panel has a main and the 2000amp is a Main Breaker.It does not fall under the tap rules because it will be a main of its own off the top side of the 2000Amp.I understand the tap rule but was wondering if this could be a main as originally it was going to be under the 2000 Amp main.I just wanted it separate so the lights could stay on in case 2000amp main needed to be turned off.
On the case of the 800 amp rule I understand you can not go up in size but according to different coursesmI have taken you can figure wire size on the 90C but can only load it to the 75C chart.In this case load is continuous so it will not be over the 80% or 1600Amps.
Thanks I am glad I found this site it provides useful info for the working Electrician.
roc1
 
They are in same control room,and will be marked by a plaque on each.My question was is it legal to tie one service off top of other main?The lighting panel will come off top of 2000amp main breaker instead of load side.The service is big enough for both?I hope this makes sense.
Thanks
roc1
 
bdarnell,

Why cant you tap ahead of the main breaker? I am thinking tapping for this new panel would actually clear up his ampacity violation because then he would have more than one disconnect and could size to the load. I dont usually work with services this big so perhaps I am missing something, but I know this is common for say a 300 amp service - one tap for a 100 amp panel, one tap for a 200 amp panel, the taps being sized for their respective mian ocpd.
 
roc1,
Is this, in fact, a "service"? From where is the MCC being fed? Is the MCC the first piece of equipment that the utility feeds?

Eric
 
If I'm not mistaken, Paralled feeders cannot simply be calculated by "adding" the individual rated ampacity in any event.

Also, it sounds as if the "service" may be installed underground? If it is, then it would require calculation based upon the 60 deg. C columb, in any event.

You must actually calculate the KCMIL, of all combined conductors, and calculate the total ohms of resistance per phase, in order to accuratly calculate the actual maximum allowable ampacity.

Keep in mind that the "total" KCMIL, cannot be equivalent to a "single" conductor of equal size, as multi or paralled conductors will create more resistance. :)
 
electric_instructor,

If I'm not mistaken, Paralled feeders cannot simply be calculated by "adding" the individual rated ampacity in any event.
Click to expand...
why do you think that?

Also, it sounds as if the "service" may be installed underground? If it is, then it would require calculation based upon the 60 deg. C columb, in any event.
Click to expand...
Without knowing the insulation type how did you come to this conclusion? I will say that I doubt the insulation type used is rated at 90 deg for underground locations most likely 75 deg which would mean any/all adjustments would start from there

You must actually calculate the KCMIL, of all combined conductors, and calculate the total ohms of resistance per phase, in order to accuratly calculate the actual maximum allowable ampacity.
Click to expand...

Well yeah, but how accurate do we need to be?



Keep in mind that the "total" KCMIL, cannot be equivalent to a "single" conductor of equal size, as multi or paralled conductors will create more resistance.
Click to expand...

Okay, you lost me on that statement. :lol:

Roger
 
electric_instructor,
If I'm not mistaken, Paralled feeders cannot simply be calculated by "adding" the individual rated ampacity in any event.
Click to expand...
That is exactly how you do it.
Don
 
electrofelon said:
bdarnell,
Why cant you tap ahead of the main breaker?
Click to expand...

My statement was in reference to 230.82. At the time I posted, I wasn't clear on whether this was a service or not. Sounds like it is.
 
It is THHN 90C wire it is in PVC Schedule 40 underground lateral service it is the service disconnect one of two 2000 amp mains in the MCC we installed.You do calculate by adding total amps of all 500 per phases together @ 90C then use 75C chart for load to make sure it is right the load is a lot less than 1600Amps per phase which is 80% for continuous load which it is.My only question is it legal to tap off line side of 2000 for Lighting panel main instead of adding 200 amp breaker to MCC.It was calculated in load on 2000 anyway.Like I said at the beggining we want lights on even if main load three phase is turned off in case of failure in MCC of some sort.
Thanks
roc1
 
Roc1
If this is indeed a service, you can tap ahead of the main disconnect on the line side. It is done all the time, and 240.21(B) is not referenced, as these are not feeder conductors.


If in fact the conductors are Type THHN and they are installed underground, you do not start the ampacity adjustment at the 90C column. Technically Type THHN is not permitted to be installed in raceways underground. You sound like a bright guy. Take a look at the definition of Location, wet in Art 100. Then take a look at 310.8, and Table 310.13.
Now also look at 240.4(C) and you will add all of the above and see that the original installation is not very compliant with the NEC.
 
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