Design Question

C

Cozzemo

Member
Location
Sacramento
Occupation
Electrician
Hi everyone,

I am hoping someone can help me with an understanding here.

I am working with the local utility for a site upgrade that involves a transformer upgrade as well.

The question I have is, can the system go from the utility provided transformer, to a meter, to a safety switch or disconnecting means, to our step up transformer, to our 800A panel. No switchgear?

Note this is not coming from utility, there was a meeting held that posed a lot of questions about the current design from our side and reducing cost. My boss is asking if we could move to a route of this nature and I just don't posses that knowledge yet.

Thank you in advance!
 
Cozzemo said:
The question I have is, can the system go from the utility provided transformer, to a meter, to a safety switch or disconnecting means, to our step up transformer, to our 800A panel. No switchgear?
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You can install the CT cabinet and meter separate from the service disconnect. This location must be acceptable to the utility.

One of the local utilities would permit the CTs to be in the padmount transformer and let you hang the meter on the side of the transformer, but other utilities in the area do not permit that.

Assuming the 800 amp panel has a main and is either outside or inside nearest the entrance of the service conductors, it should be fine.
 
zbang said:
Not what you asked, but step-UP? Usually it's easier to get higher voltages and step down as needed.
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Utility will only bring us 208, property currently has 240V equipment. I am not sure why they won't drop 240V to us but that is what we are dealing with.
don_resqcapt19 said:
You can install the CT cabinet and meter separate from the service disconnect. This location must be acceptable to the utility.

One of the local utilities would permit the CTs to be in the padmount transformer and let you hang the meter on the side of the transformer, but other utilities in the area do not permit that.

Assuming the 800 amp panel has a main and is either outside or inside nearest the entrance of the service conductors, it should be fine.
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That 800 amp panel does have a main, it would be installed inside. I appreciate the clarification a ton.
 
Cozzemo said:
Utility will only bring us 208, property currently has 240V equipment. I am not sure why they won't drop 240V to us but that is what we are dealing with.
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Exactly where is the step up transformer in this set up? I am assuming the step up transformer is customer owned.
 
Cozzemo said:
The question I have is, can the system go from the utility provided transformer, to a meter, to a safety switch or disconnecting means, to our step up transformer, to our 800A panel. No switchgear?
Click to expand...

Sure, is there something specific you are concerned about?

You just want to check to see if the utility has any specific requirements. For example, one utility I know requires services over a certain size land in a metering section of a switchboard or switch gear.
 
Utility transformer -> CT/Meter -> Service disconnect -> Transformer -> Panel. N-G bond would be in the service disconnect. Do a high-leg delta panel and make sure to label the B phase as 240V. Depending on location of transformer, like Don said you may need an additional primary disconnect.
 
tjdilly said:
Utility transformer -> CT/Meter -> Service disconnect -> Transformer -> Panel. N-G bond would be in the service disconnect. Do a high-leg delta panel and make sure to label the B phase as 240V. Depending on location of transformer, like Don said you may need an additional primary disconnect.
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This is why I ask:


There are better ways to do this.
 
steve66 said:
This is why I ask:


There are better ways to do this.
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Huh. Had no idea this was an issue. Admittedly I've not been involved much with 240V high-leg 120V loads (Thankfully it's falling out of the norm). I've seen dozens of older facilities absolutely loaded to the max with 120V loads on a center tapped transformer. Does this actually happen, or is this a manufacturer CYA note? Maybe they balanced them less than 5%? I doubt it, considering the state of the installs...
 
tjdilly said:
Huh. Had no idea this was an issue. Admittedly I've not been involved much with 240V high-leg 120V loads (Thankfully it's falling out of the norm). I've seen dozens of older facilities absolutely loaded to the max with 120V loads on a center tapped transformer. Does this actually happen, or is this a manufacturer CYA note? Maybe they balanced them less than 5%? I doubt it, considering the state of the installs...
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This is only a issue with a three phase transformer. Most 4 wire high leg deltas I have seen are made of using 2 or 3 single phase transformers and the line to neutral load is not an issue. It is based on the KVA of the transformer that supplies the 120/240. For utility supplied systems, you will often see one of the transformers is larger than the others. It is sized to supply the 3 phase load and the 120/240 single phase load.
 
don_resqcapt19 said:
This is only a issue with a three phase transformer. Most 4 wire high leg deltas I have seen are made of using 2 or 3 single phase transformers and the line to neutral load is not an issue. It is based on the KVA of the transformer that supplies the 120/240. For utility supplied systems, you will often see one of the transformers is larger than the others. It is sized to supply the 3 phase load and the 120/240 single phase load.
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Right, I'm specifically talking about an incoming 480V service with a non-utility, high-leg, 3-phase transformer. I don't even think about the transformers if it's utility owned ;).
 
tjdilly said:
Right, I'm specifically talking about an incoming 480V service with a non-utility, high-leg, 3-phase transformer. I don't even think about the transformers if it's utility owned ;).
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If you need more than 5% for the line to neutral loads, you will have to use two or 3 transformers to create a 3 phase bank. A far as I know all 3 phase transformers that can supply a 4 wire high leg system as limited to 5% for the line to neutral loads.
 
tjdilly said:
Right, I'm specifically talking about an incoming 480V service with a non-utility, high-leg, 3-phase transformer. I don't even think about the transformers if it's utility owned ;).
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If it is non-utility owned it is not a service.
For customer owned transformers, I have seen customer made closed delta designed to handle a 100% imbalance, but it is much more common to supply an open delta bank even if it is in a single enclosure.
 
don_resqcapt19 said:
This is only a issue with a three phase transformer. Most 4 wire high leg deltas I have seen are made of using 2 or 3 single phase transformers and the line to neutral load is not an issue. It is based on the KVA of the transformer that supplies the 120/240. For utility supplied systems, you will often see one of the transformers is larger than the others. It is sized to supply the 3 phase load and the 120/240 single phase load.
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Agree - most high leg systems are created at the utility with 3 single phase utility transformers on a pole. But I'm assuming we are talking about converting the regular 208 utility service to a high leg with a single, three phase, dry type transformer.

Without knowing exactly what the loads are, and what needs 240V, why not just provide 240 for the loads that really need it (if there even are any loads that aren't dual rated 240/208) , and leave everything else as a 208/120V?

And boost transformers or solid state drives might be other options for boosting the voltage for certain loads.

One big 800A, 3 phase transformer just seems like a sledgehammer approach.
 
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