small pool and spa motors VD calcs

[GISdude]

Hey all.
I work for the local utility. I have a customer who installed a pool and pool house with a spa and a gazebo (in addition to his unoccupied, almost finished 7000 sq. ft house). The electrician installed a 400A main breaker for the pool and pool house, however it's 500' ft away from the 25 kVA pole-bolted XFRM! His load doesn't look bad(2 1.5 hp pumps, some lighting for the gazebo and the small pool room/guest house). Normally, we as the utility won't allow a customer to go more than 250' from the point of connection. I was doing some VD calcs and came out to about 7% w/ a 500' run of 4/0 al. We are not supposed to allow more than 5% VD thru the secondary and service. That was NOT knowing what the NEMA code letter was on the 2 motors.
My question is, should he up the wire to 350mcm? Usually we won't go that big, but I'm thinking the electrician is going to have to run that anyways, short of moving his meter panel 250' closer.
I'm not an electrician, just a designer, but it seems to me it might be cheaper for the electrician to just move the panel.

Sorry for the long post.

 

[gar]

080605-0802 EST

GISdude:

From one source I found 0000 Al wire to be 0.08 ohms per 1000 ft and that is your loop length.

Suppose you only use a neutral and one 120 V hot wire to the pool area and total normal load was 5 KVA, then the current is about 42 A. For this current the total voltage drop would be 3.4 V and that is 2.8 %. If both 120 V phases are sent to the pool area, then equally distributing the load will cut the voltage drop in half per 120 side. I am guessing that for two 1.5 HP motors on at the same time you would see about 3 KVA load. If you double my 5 KVA estimate to 10 KVA, then you double the above values.

Why would you ever use a 400 A breaker feeding this very light load at the pool? Of course my 5 KVA was a guess on the load from your broad comments on what would be at the pool. There needs to be a more specific definition of the expected peak load.

Another possibility is to feed 240 to the pool area, use the same wires, and use a step down transformer to 120.

.

 

[bob]

Hey all.
The electrician installed a 400A main breaker for the pool and pool house, however it's 500' ft away from the 25 kVA pole-bolted XFRM! His load doesn't look bad(2 1.5 hp pumps, some lighting for the gazebo and the small pool room/guest house). Normally, we as the utility won't allow a customer to go more than 250' from the point of connection.

I don't want to sound rude, but what gives you the right to dictate what someone does on his property. As long as you have proper voltage at the meter, that's the end of you responsibility.

I was doing some VD calcs and came out to about 7% w/ a 500' run of 4/0 al. We are not supposed to allow more than 5% VD thru the secondary and service. That was NOT knowing what the NEMA code letter was on the 2 motors.

What load is used for the voltage drop calculation? Is the 4/0 the
utilities conductor? If you have secondary conductors involved why not
locate the transformer closer? The NEMA code letter is used for flicker calculations and not voltage drop.

My question is, should he up the wire to 350mcm? Usually we won't go that big, but I'm thinking the electrician is going to have to run that anyways, short of moving his meter panel 250' closer.
I'm not an electrician, just a designer, but it seems to me it might be cheaper for the electrician to just move the panel.

Why don't you move the transformer closer? I will agree that 500 ft is a long
way. I wasn't aware that the utility was in the business of designing the customers electrical facilities.
Again you don't list the loads used in the VD calculations. Are you using the calculated load required by the NEC in 220? I would like to see them.
Using 100 amps single phase at 500 ft , VD 4/0 AL = 5.0% VD 4/0 CU = 2.6%.

 

[LarryFine]

Why don't you move the transformer closer?

My thought exactly. You should have been the first to suggest it. I often do and the power co. is the one who resists.

 

[GISdude]

I don't want to sound rude, but what gives you the right to dictate what someone does on his property. As long as you have proper voltage at the meter, that's the end of you responsibility.

You're right, however his meter panel is 500' away from the secondary box. Technically we require it to be 250' or shorter from the box - there's a little "wiggle room" in the 250', but 500' is just way too long.

Why don't you move the transformer closer? I will agree that 500 ft is a long
way. I wasn't aware that the utility was in the business of designing the customers electrical facilities.

I don't want to design the electrical facilities - I got enough on my plate. I'm trying to be flexible. When you APPLY for power, you agree to abide by the rules/regs that the utility has established. He's already broken 1 rule - going 250' away from the point-of-connection.

I appreciate the feedback on this. I'm thinking the best thing is to put in 350mcm. In this case he doesn't have to open up his trench and show the depth that he was supposed to install it the conduit at.

Thanks again guys

 

[bob]

You're right, however his meter panel is 500' away from the secondary box. Technically we require it to be 250' or shorter from the box - there's a little "wiggle room" in the 250', but 500' is just way too long.

Is this house located in a subdivision with underground electrical utilities?

 

[GISdude]

subdivision location

subdivision location

This house is in a rural area where the average lot size is 5 ac. He's almost finished construction on the 7000 sq ft house. He is being fed by a 25 kVA pole-bolted XFRM and it looks like all we got out there (for the most part) is OH. This guy is even willing to change out the 25 kVA for a 50 kVA just so he can keep his pool!
I wish I had the cash for that!