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New 200A residential service voltage drop

2681 Views 7 Replies 3 Participants Last post by  emtnut
Wondering about the rules on this. House load is about 60 Amps but plan on adding a future garage/shop. Here's the info I have:

Transformer to meter on the house is 360 ft buried.
cable is 3c 4/0 aluminum
Regular 240 v service for the house
load is 60 A for now

Inspector came through and said today that i have to downsize main to 100 A or pull 350 kcmil wires for the 200A panel instead. He said based on the numbers I was sitting at a 13% volt drop from the pole to the house. Based on CEC table d3 ive done the calculations based on the max distance allowed and have never come close to 13 % drop at this distance. Not sure if im missing something?

Any experience in this would help.
not sure how he got to 13%.

Thanks.
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Wondering about the rules on this. House load is about 60 Amps but plan on adding a future garage/shop. Here's the info I have:

Transformer to meter on the house is 360 ft buried.
cable is 3c 4/0 aluminum
Regular 240 v service for the house
load is 60 A for now

Inspector came through and said today that i have to downsize main to 100 A or pull 350 kcmil wires for the 200A panel instead. He said based on the numbers I was sitting at a 13% volt drop from the pole to the house. Based on CEC table d3 ive done the calculations based on the max distance allowed and have never come close to 13 % drop at this distance. Not sure if im missing something?

Any experience in this would help.
not sure how he got to 13%.

Thanks.
What load are you using in your calc’s?
 

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Discussion Starter · #3 ·
Wondering about the rules on this. House load is about 60 Amps but plan on adding a future garage/shop. Here's the info I have:

Transformer to meter on the house is 360 ft buried.
cable is 3c 4/0 aluminum
Regular 240 v service for the house
load is 60 A for now

Inspector came through and said today that i have to downsize main to 100 A or pull 350 kcmil wires for the 200A panel instead. He said based on the numbers I was sitting at a 13% volt drop from the pole to the house. Based on CEC table d3 ive done the calculations based on the max distance allowed and have never come close to 13 % drop at this distance. Not sure if im missing something?

Any experience in this would help.
not sure how he got to 13%.

Thanks.
What load are you using in your calc’s?


I've done calcs with both just to see the difference. 60 A and 160 A. Based on rule saying use 80 %if load is unknown.
 

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I've done calcs with both just to see the difference. 60 A and 160 A. Based on rule saying use 80 %if load is unknown.
I just did a quick calc at 200 amps with 4/0 aluminum I get around 200 ft max with a 3 % drop.

At 100 amps and 4/0 aluminum I get 390 feet max at 3% drop.

I’d say the inspector is correct.

Can you show me how your calculating it?
 

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Also keep in mind the rule is 5% from service connection to furthest outlet and 3% from the panel to furthest outlet. So on the line side of the service panel you should have 2% drop or less.
 

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Discussion Starter · #6 ·
I've done calcs with both just to see the difference. 60 A and 160 A. Based on rule saying use 80 %if load is unknown.
I just did a quick calc at 200 amps with 4/0 aluminum I get around 200 ft max with a 3 % drop.

At 100 amps and 4/0 aluminum I get 390 feet max at 3% drop.

I’d say the inspector is correct.

Can you show me how your calculating it?
From d3 equation

Using a load of 60 amps 90 degree cable at 3% drop I did

31.6m x 3% x 1.08 x (240/120) = 204 meters max

Using 160 amp load (80% of main) I did

12.4m x 3% x 1 x (240/120) = 74.4 meters max.

I no I'm under on the distance on the second length for 3% but I'm still wondering how he got to 13 % loss when I'm at 3 % after roughly 200 ft.
Also he had the load calc so I assume he used 60 a not 160. But no 100 %sure.
 

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Not sure where he got 13% either but the fact is you are undersized for a 200 amp service at that length with 4/0 aluminum.

You also can not use the load calc (60 amps) to size the conductors on a service. You must size them to take the full load. The rating of the service is the overcurrent or the ampacity of the conductors, whichever is less. 8-104(1)

A load calc on a house is considered a non continuous load. The customer can add load in the future up to 100% of the main following the load calc rules of 8-200. If the conductors for the service can not carry the full load of the service overcurrent rating, (like when using table 39 for instance) there must be a permanent label on the panel stating what the max load allowed on the service is.
 

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Agree with Incognito, Inspector is right.

I guess the only question is did he say 13% and meant 13V
or did he say 13V and you heard %

Just do your voltage drop calc for the 200A service, upsize conductors, get sticker.
 
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