480v disconnect

[hartr082988]

Im replacing an underground service where the sub pole is 1000' away. At the pole I have the 200amp meter main disco to a transformer right next to pole to jump up to 480v for voltage loss over the 1000'. Then into a disco and another step down transformer by the house before going into the panel. My question is does the disco for the step down transformer have to be fusible? Having a hard time finding fused 480v 200 amp 2 phase disco.

 

[electrofelon]

Im replacing an underground service where the sub pole is 1000' away. At the pole I have the 200amp meter main disco to a transformer right next to pole to jump up to 480v for voltage loss over the 1000'. Then into a disco and another step down transformer by the house before going into the panel. My question is does the disco for the step down transformer have to be fusible? Having a hard time finding fused 480v 200 amp 2 phase disco.

Yes you need primary protection for the transformer. Unfortunately there is not an allowance in the code to use the previous transformer's protection to protect this one.

 

[electrofelon]

Just curious what exactly are you doing there? You say "replacing". So this was existing? What are you upgrading to? I would strongly advise against step up step down for this length if it's not too late. Not cost effective at this length and you will have poor power quality with a wide voltage swing.

 

[hartr082988]

Yes you need primary protection for the transformer. Unfortunately there is not an allowance in the code to use the previous transformer's protection to protect this one.

I understand I need one, don't want someone having to run 1000' to shut it down. My question is, does it have to be fusible? I can find unfused disco but not fused.

 

[infinity]

I understand I need one, don't want someone having to run 1000' to shut it down. My question is, does it have to be fusible? I can find unfused disco but not fused.

So you have a single phase step-up SDS feeding another step-down SDS on the other end?

 

[electrofelon]

I understand I need one, don't want someone having to run 1000' to shut it down. My question is, does it have to be fusible? I can find unfused disco but not fused.

Actually the disconnecting means can be remote as long as it's labeled and lockable. However there are other ocpd requirements, transformer secondary conductors and transformer protection. So yes it needs ocpd.
See 450.3 B and 240.21(C)

 

[infinity]

Since this is outside there is no limit as to the length of the secondary conductors before they terminate at the OCPD. Take a look at 240.21(C)(4).

Just for conversation is this going to be a single phase 480 ungrounded system?

 

[electrofelon]

Since this is outside there is no limit as to the length of the secondary conductors before they terminate at the OCPD. Take a look at 240.21(C)(4).

Just for conversation is this going to be a single phase 480 ungrounded system?

And the secondary conductors can be protected by the primary overcurrent device, but I don't see any way around the 450.3 B protection for the second transformer. When I do these with pad Mount transformers, they have fusing built-in which is nice.

 

[electrofelon]

Just for conversation is this going to be a single phase 480 ungrounded system?

The best way to do these is ground one end, and use the exception (250.30(A) something?) that allows using the ground to conductor as the bonding conductor, so only two wires are needed

 

[kwired]

Since this is outside there is no limit as to the length of the secondary conductors before they terminate at the OCPD. Take a look at 240.21(C)(4).

Just for conversation is this going to be a single phase 480 ungrounded system?

Doesn't such setup qualify to use just two conductors and bond one of them if there is no other potential parallel paths between the ends? I have no idea if that is still allowed in 2023 NEC.

 

[kwired]

The best way to do these is ground one end, and use the exception (250.30(A) something?) that allows using the ground to conductor as the bonding conductor, so only two wires are needed

You posted while I was writing my post

 

[kwired]

And the secondary conductors can be protected by the primary overcurrent device, but I don't see any way around the 450.3 B protection for the second transformer. When I do these with pad Mount transformers, they have fusing built-in which is nice.

But if you were feeding some other load(s) with that secondary it is considered to have overcurrent protection equal to the primary protection times the transformer voltage ratio, so is there some reason why it will not still have same protection level if it supplies another transformer?

 

[electrofelon]

But if you were feeding some other load(s) with that secondary it is considered to have overcurrent protection equal to the primary protection times the transformer voltage ratio, so is there some reason why it will not still have same protection level if it supplies another transformer?

Yes of course in theory it is protected, I am just not seeing an allowance in the code for it. I guess you could plead common sense to the AHJ

 

[hillbilly1]

Im replacing an underground service where the sub pole is 1000' away. At the pole I have the 200amp meter main disco to a transformer right next to pole to jump up to 480v for voltage loss over the 1000'. Then into a disco and another step down transformer by the house before going into the panel. My question is does the disco for the step down transformer have to be fusible? Having a hard time finding fused 480v 200 amp 2 phase disco.

Why are you using a 200 amp disconnect on the 480 side? A 100 amp would be sufficient. If you need greater than 100 amp, a three pole 200 with two fuses will work.

 

[tortuga]

Having a hard time finding fused 480v 200 amp 2 phase disco.

You probably need to search for a 600V 2 pole fused disconnect, not a 480V two phase,
You can just use a 3 phase and omit a phase for example a Siemens HF364R
Searching for a '2 phase disconnect' will in most cases get you a 4 pole disconnect.

 

[hartr082988]

Just curious what exactly are you doing there? You say "replacing". So this was existing? What are you upgrading to? I would strongly advise against step up step down for this length if it's not too late. Not cost effective at this length and you will have poor power quality with a wide voltage swing.

It's an 40 year old 100 amp direct bury #1 aluminum service. I'd need 750 kcmil to account for voltage loss over 1000'. This was the cheaper solution to upgrade to 200 amp.

 

[hartr082988]

So you have a single phase step-up SDS feeding another step-down SDS on the other end?

correct

 

[hartr082988]

You probably need to search for a 600V 2 pole fused disconnect, not a 480V two phase,
You can just use a 3 phase and omit a phase for example a Siemens HF364R
Searching for a '2 phase disconnect' will in most cases get you a 4 pole disconnect.

I thought they existed but that was my thought as well.

 

[hartr082988]

Since this is outside there is no limit as to the length of the secondary conductors before they terminate at the OCPD. Take a look at 240.21(C)(4).

Just for conversation is this going to be a single phase 480 ungrounded system?

I am going to run 4/0 quadplex in conduit to keep ground continuous from forst means of disconnect which would be the meter main on sub pole.

 

[hartr082988]

Why are you using a 200 amp disconnect on the 480 side? A 100 amp would be sufficient. If you need greater than 100 amp, a three pole 200 with two fuses will work.

It's for a 200 amp service. If the load is over a 100 amps, which it will be, I assume 100 amp fuses won't be sufficient.