Downgrading a service from 480V to 240V three phase

[jaylectricity]

I've got a 480V MDP that used to feed some bus ducts. It still feeds two other panels after being stepped down by three separate transformers. The other panels are a 120/240V single phase and a 120/240V three phase. Customer wants to downgrade the power to get rid of the transformers and to not have 480V coming into the building. It's a toolshop/warehouse that's being turned into an office building. One of the transformers makes a ton of noise and he's worried about the liability of having regular cubicle jockeys around so much power.

My plan is to have the poco change the drop to just a 120/240 three phase, eliminate the transformers and refeed the two existing panels from the main panel. Does this sound doable or am I looking at replacing all the service equipment?

This would be the largest service I've ever worked on, but I understand what needs to happen, just not sure of the nuts and bolts of it. I'm wondering if breakers are still available for the existing equipment. Sorry I don't have a manufacturer, but they aren't simple 1" plug-in or bolt-on breakers like the several subpanels throughout the building.

Also, obviously I would have the POCO disconnect power to the building while I worked on it, then reenergize after inspection. Just looking to ballpark a price within a couple thousand dollars for the customer.

 

[petersonra]

I've got a 480V MDP that used to feed some bus ducts. It still feeds two other panels after being stepped down by three separate transformers. The other panels are a 120/240V single phase and a 120/240V three phase. Customer wants to downgrade the power to get rid of the transformers and to not have 480V coming into the building. It's a toolshop/warehouse that's being turned into an office building. One of the transformers makes a ton of noise and he's worried about the liability of having regular cubicle jockeys around so much power.

My plan is to have the poco change the drop to just a 120/240 three phase, eliminate the transformers and refeed the two existing panels from the main panel. Does this sound doable or am I looking at replacing all the service equipment?

This would be the largest service I've ever worked on, but I understand what needs to happen, just not sure of the nuts and bolts of it. I'm wondering if breakers are still available for the existing equipment. Sorry I don't have a manufacturer, but they aren't simple 1" plug-in or bolt-on breakers like the several subpanels throughout the building.

Also, obviously I would have the POCO disconnect power to the building while I worked on it, then reenergize after inspection. Just looking to ballpark a price within a couple thousand dollars for the customer.

what is 120/240 3 phase?

how big of a service is it? how big of a service will he need after the conversion.

you should first reassure him that the voltage level coming into the building does not significantly affect its safety. They are just as likely to die from mishandling 240V as 480V. that way he can make an informed decision and not panic based on an erroneous belief he is making the place safer.

it is also quite possible that his electricity cost would go up, along with having to pay a bunch of money for the privilege of paying more for the juice afterward.

If the service does get replaced, it is probably a good idea to just replace the service equipment rather than try and buy used stuff to fit in the old boxes. It is also probably a good time to look very closely at the system as a whole.

In the end all you might need is a fused disconnect as the service equipment.

if a transformer is making noise, it is sometimes something as simple as a cover that is not screwed on tightly, or that is vibrating against the floor or a conduit.

 

[kwired]

First thing, are you eliminating or converting all 277 and/or 480 volt loads? Don't forget any existing HVAC or 277 volt lighting.

Otherwise it won't hurt and is not a violation to connect 120/240 volts to 480 volt rated breakers, switchgear etc.

 

[GoldDigger]

Your mention of 120/240 three phase implies a high leg 240 delta service. Many POCOs will not supply that configuration as a new service. See what your POCO is willing to provide before spending too much time planning.

 

[iwire]

You will get 208Y/120 3 phase most likely

 

[jaylectricity]

what is 120/240 3 phase?

208v, whatever

how big of a service is it? how big of a service will he need after the conversion.

480V 2000A existing. He probably only needs the equivalent of 600A at 240v, however that translates to three phase.

it is also quite possible that his electricity cost would go up, along with having to pay a bunch of money for the privilege of paying more for the juice afterward.

If the service does get replaced, it is probably a good idea to just replace the service equipment rather than try and buy used stuff to fit in the old boxes. It is also probably a good time to look very closely at the system as a whole.

In the end all you might need is a fused disconnect as the service equipment.

if a transformer is making noise, it is sometimes something as simple as a cover that is not screwed on tightly, or that is vibrating against the floor or a conduit.

Transformer is on a shelf, but I can look into tightening screws.

Why would the electrical cost go up?

 

[iwire]

BTW, the power co may well bill the customer for the new trans and labor to put it in. I would not expect it to be cheap.

 

[jaylectricity]

First thing, are you eliminating or converting all 277 and/or 480 volt loads? Don't forget any existing HVAC or 277 volt lighting.

Otherwise it won't hurt and is not a violation to connect 120/240 volts to 480 volt rated breakers, switchgear etc.

I do believe all 277 and 480V loads are eliminated. All lighting and HVAC goes through the other two panels after the transformers.

 

[jaylectricity]

BTW, the power co may well bill the customer for the new trans and labor to put it in. I would not expect it to be cheap.

Yeah, that would be part of the estimating a cost. Originally he was hoping to split up the service into separate meters for each side of the building so the tenant could pay their own bill, but I don't think it will benefit him to do so because so much of the existing load is mixed between all the various panels.

 

[Iron_Ben]

My plan is to have the poco change the drop to just a 120/240 three phase, eliminate the transformers and refeed the two existing panels from the main panel.

Have you spoken to the poco? From their point of view they are being asked to completely rework a service for no good reason. Incremental revenue increase for them = zero. Believe it or not, this a several thousand dollar job for them. If it's say, $4,000, they'd likely insist on full payment up front. We would have.

We had a load limit on 240/120 wild leg three phase services of 600 amps. Other utilities may or may not have a similar policy. So if they do, and this is a 400 amp or larger 480 service, it's not likely to fly. Just some fun things to consider......

 

[jaylectricity]

Your mention of 120/240 three phase implies a high leg 240 delta service. Many POCOs will not supply that configuration as a new service. See what your POCO is willing to provide before spending too much time planning.

I'm not positive that's what it is. I just checked my notes and the panel was labeled as 230V 3P. Probably should have taken a picture.

 

[jaylectricity]

Have you spoken to the poco? From their point of view they are being asked to completely rework a service for no good reason. Incremental revenue increase for them = zero. Believe it or not, this a several thousand dollar job for them. If it's say, $4,000, they'd likely insist on full payment up front. We would have.

We had a load limit on 240/120 wild leg three phase services of 600 amps. Other utilities may or may not have a similar policy. So if they do, and this is a 400 amp or larger 480 service, it's not likely to fly. Just some fun things to consider......

I fully expect to pay them to change transformers. I don't see any reason to change the conductors.

 

[ron]

Since the service entrance POCO will change the transformer configuration on their end, be sure the panel you plan to reuse, and anything downstream, has the proper short circuit ratings.

 

[Jraef]

... We had a load limit on 240/120 wild leg three phase services of 600 amps. Other utilities may or may not have a similar policy. So if they do, and this is a 400 amp or larger 480 service, it's not likely to fly. Just some fun things to consider......

MOST utilities, if they even ALLOW it for a new service, will have a load limit on a 120/240 3 phase 4 wire service. This type of service is intended for customers who have a MAJORITY of 3 phase 230V loads, but also need a SMALL AMOUNT of 120V available for lights and plugs. So in many cases the 120V loading is limited to 5% of the transformer capacity.

If ALL of his loads are 120V, that means a HUGE transformer (if they would even consider it). Your utility will most likely want you to use a 208Y120V service if most of the loads are 120V so that you can balance out the distribution of the 120V loads evenly between phases. But then you have to evaluate the effect on any 240V equipment. Most of the time it's fine, you just need to check.

 

[jaylectricity]

Well, the transformers that are installed within the building are each about 3'X3'X3' and there's three of them. Is that "huge"?

I believe most of the loads are going to be 120V since it will mostly be lighting, computer desks, communications, etc.

Thanks for the info, I'll have more to digest with this.

 

[GoldDigger]

FWIW,
1. Keeping the existing transformers will have an energy cost since they are on the customer side of the meter.
2. They may not actually be large enough for the lighting and office machine load of the new usage, if the machine shop did not have a lot of 240V loads.

 

[Jraef]

Well, the transformers that are installed within the building are each about 3'X3'X3' and there's three of them. Is that "huge"?

I believe most of the loads are going to be 120V since it will mostly be lighting, computer desks, communications, etc.

Thanks for the info, I'll have more to digest with this.

I didn't mean physically huge (although that too).

If you had a 600A 240/120 single phase service, but all of the loads are 120V, to get that from a 3 phase 4 wire delta transformer that is limited to 5% of it's capacity being 120V loads, the transformer would have to be capable of 12,000A, so you are talking about a 5,000kVA transformer!

My point in bringing this up is to highlight that fact that a 120/240 3 phase 4 wire delta transformer arrangement is NOT likely going to fly as a way to get 120V SINGLE phase loads of that magnitude.

 

[kwired]

Keeping existing service as is may have some high monthly charges as well if the demand is well below what it once was. We are apparently going from 2000 amp 480 volt three phase (but not knowing what original demand was) to 600 amp 240 volt (single phase?) sounding like it has enough capacity. So possibly going from 1500 kVA down to only 150 kVA with utility transformer.

 

[Iron_Ben]

I didn't mean physically huge (although that too).

If you had a 600A 240/120 single phase service, but all of the loads are 120V, to get that from a 3 phase 4 wire delta transformer that is limited to 5% of it's capacity being 120V loads, the transformer would have to be capable of 12,000A, so you are talking about a 5,000kVA transformer!

Not true if an open delta arrangement is used. I recall a small to medium size Piggly Wiggly grocery store that we served, built in the 60's. The load was mostly single phase, with some three phase for the largest freezers. We amped the service one hot summer day and the phase readings were along the lines of 450, 430, and 100 on the stinger leg, something like that. The bank was either a 100 and a 25 or a 75 and a 25, can't recall.

We had many (several hundred) overhead delta banks in service in the older part of town. Maybe 70% of them were three pot closed delta and 30% two pot open delta. The larger ones might serve 20 or more apartments (single phase) and a few businesses (three phase). Or a church (three phase) and 4 or 5 homes (single phase). Unless we amped the conductors we had no idea how balanced or unbalanced things were. No clue as to how much load was 120 volt single phase, 240 volt single phase or 240 volt three phase. The few times we did so, the readings were usually a bit more balanced than the grocery store above but still way unbalanced. I know we had at least one big bank, a 100 and two 50's, that served around 20 apartments. The load was all single phase as the one or two three phase customers that had been on it originally were no longer in business. Should we have reworked the bank to just one transformer? - you bet. But there were always other fires to put out.

I *much* prefer a wye service, 208Y/120 or 480Y/277. I strongly discouraged new delta services but we did provide them up to 600 amps (and a surprising amount of engineers requested them). But in fairness I must admit that company wide we had thousands of high leg services from back in the Stone Age, all still going strong, many of them 50 and 60 years later.

 

[kwired]

Not true if an open delta arrangement is used. I recall a small to medium size Piggly Wiggly grocery store that we served, built in the 60's. The load was mostly single phase, with some three phase for the largest freezers. We amped the service one hot summer day and the phase readings were along the lines of 450, 430, and 100 on the stinger leg, something like that. The bank was either a 100 and a 25 or a 75 and a 25, can't recall.

We had many (several hundred) overhead delta banks in service in the older part of town. Maybe 70% of them were three pot closed delta and 30% two pot open delta. The larger ones might serve 20 or more apartments (single phase) and a few businesses (three phase). Or a church (three phase) and 4 or 5 homes (single phase). Unless we amped the conductors we had no idea how balanced or unbalanced things were. No clue as to how much load was 120 volt single phase, 240 volt single phase or 240 volt three phase. The few times we did so, the readings were usually a bit more balanced than the grocery store above but still way unbalanced. I know we had at least one big bank, a 100 and two 50's, that served around 20 apartments. The load was all single phase as the one or two three phase customers that had been on it originally were no longer in business. Should we have reworked the bank to just one transformer? - you bet. But there were always other fires to put out.

I *much* prefer a wye service, 208Y/120 or 480Y/277. I strongly discouraged new delta services but we did provide them up to 600 amps (and a surprising amount of engineers requested them). But in fairness I must admit that company wide we had thousands of high leg services from back in the Stone Age, all still going strong, many of them 50 and 60 years later.

You have a lot of flexibility with a "bank", and can more easily customize it to your needs. Typical "off the shelf" padmount units however will likely be three coils of equal kVA rating but all your 120 volt load is only on one of them.