MEP 805B wired to split 400amp panels

[87cr250r]

A lot of people are moving away from the expensive metal bodied pin and sleeve connectors. The marine industry is moving to disconnect duty connectors. They're about 75% of the price of the metal connectors but much less expensive overall to install as they don't require a disconnect switch.

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[MDdeuce]

There should only be 3-conductors to the genset as the neutral (L0) doesn't get connected. Is your 4th conductor the safety ground (GND)?

I was originally planning 5 conductors in the feeder from the set, L1, L2, L3, L0, GND. L0 was needed for the 120v circuits, and was running GND so I wouldn't need to worry about a ground rod at the gen set (pulling from service entry ground). With the transformer don't need L0 anymore, so only 4 conductors. Makes the feeder cheaper.

 

[MDdeuce]

TommyTone, have you already sourced ( or located a source for ) the pin and sleeve connectors? Curious what you found as last time I was looking for them for an unrelated project I almost fell off my chair when the price popped up on the screen! Think the cheapest I found was over $600 per half, with some being well over $1000 per half. Needless to say that project went down an alternate path, veering away from the pin and sleeve connectors.

I was looking at the Scame branded pin and sleeve connectors from elecdirect. They're expensive, but not $1000 per half expensive.

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[Ray70]

Ah yes, a bit pricey, but way cheaper than Hubbell!

 

[MDdeuce]

So surplus/salvage 3P equipment does not seem to be readily available in my area. All of the supply places I called either didn't carry this stuff or could only order new, and none of them had ideas about who would carry it. I was able to find one randomly on a re-selling site that is semi local and a reasonable price. However, it is a 63kVA 460 delta to 460/266 wye.

So, question is, since this has the same winding ratios as a 208 delta to 208/120 wye, will this work the same at 208, or is there extra magic inside 3P transformers with the delta to wye configuration that the voltage operation will not transfer like 1P transformers? My understanding from looking at the basic 3P transformer design equations is that it should operate the same at 208 as it does 460, and since I'd be operating under the kVA and voltage ratings all would be fine.

 

[Scoobyshep]

Winding primary/winding seccondary=voltage primary/ voltage secondary= current secondary/current primary

A 3 phase transformer is just 3 single phase transformers in the same case. If you lower the primary voltage the secondary voltage will drop by the winding ratio. Some transformers are tappable there are voltage adjustment taps ro correct for off spec voltage.

 

[Tommytone]

TommyTone, have you already sourced ( or located a source for ) the pin and sleeve connectors? Curious what you found as last time I was looking for them for an unrelated project I almost fell off my chair when the price popped up on the screen! Think the cheapest I found was over $600 per half, with some being well over $1000 per half. Needless to say that project went down an alternate path, veering away from the pin and sleeve connectors.

Yes. One arrived today and one other plug this week as well as 4 receptacles. They were around $130 for the plugs each. The receptacles were under $50. I got them through ebay. The receptacles were takeouts and the plugs are new minus box on one and open box on the other.

Regardless of how I do it this was the cheapest way short of trying to hardwire every time which is a recipe for error.

 

[MDdeuce]

Picked up a 3P isolation transformer. Now just need to get wire, connectors, and such and wire it all up.

 

[Scoobyshep]

Picked up a 3P isolation transformer. Now just need to get wire, connectors, and such and wire it all up.

View attachment 885958

Remember to bond the transformer output

 

[pclausen]

I don't have 3 phase 400A, but I do have 2 phase 400A with both a 400A disconnect as well as a 400A transfer switch.

Here's how I wired mine:



500 MCM Al coming up into the meter base on far left. From there's its all 300 MCM Cu, except ground which is 1/0 Al.

Here it is with all the covers in place:



Here's a very simplified diagram of the layout:



House has 2 200A sub-panels and the shop has a single 200A sub-panel as well as a 225A solar sub-panel (I have 60 kW worth of solar arrays).

I actually have 2 generators, a MEP 803A and a Kubota 20 kW. I can switch between them with a manual 100A transfer switch.

The only place in the whole system where Neutral and GND are bonded is in the 400A disconnect switch:



Did all the work myself and had the county come out and inspect. Dual ground rods and the shop and the house. 200' run between the shop and the house, using 3x 500 MCM Al with 1/0 GND.

POCO made me put in 3" conduit for the run from the pole to the meter base. They didn't require that when I did this 20 years ago, but this year they did.



Got a 50 KVA transformer on the pole going up to 14.4kV. Main reason for the 50 KVA transformer is not so much what I consume, but being able to handle me pushing 60 kW into the grid during the summer months.

 

[MDdeuce]

After the good discussion in this thread I’ve revised my design a little bit. Below is the diagram of what I’m planning on doing. Welcome any comments and suggestions.



After the holidays I plan to start ordering the bits and get this install rolling before we have a serious outage and I have 15kWs sitting in the driveway I can’t use. Just last week there was a nasty car accident that took out a pole and the other side of the state road lost power for 18-24hrs overnight with temps in the low 20s.

I’ve also been reading the NEC some. My county has adopted NEC 2020, and while I haven’t decided if I’m pulling permits I do want to ensure that this install is fundamentally safe, and meets code. I have a few questions that I’m sure some of you will probably know the answers too. I’m also probably going to call the electrician that wired the house and pay him a few hours time to review this and do a walk through after I install.

Questions:
-with the 3P transformer is this still considered a non-SDS source? The GND is continuous across the system, but neutral now is not. The only earth ground is the service entry, and the only L0-GND bond is at the gen service terminals on the primary side and in the panels on the secondary side. To meet code would this need to be a SDS source and have a separate earth ground at the gen and break the ground at the transformer?
-I’ve fused L1/L2/L3 at 60A and running 6AWG THHN on the secondary side rated at 75A. Should I bump up the L0 conductor since many of the loads will be 120v loads using the neutral?
-NEC states that gens must be UL listed. Pretty sure MEPs are non-UL, can anybody confirm? This seems like an instant permit fail on a technicality.
-NEC requires a generator disconnect, does the MEP built in contactor meet this requirement? I included a fused disconnect incase it doesn't, and having it is probably a good idea anyways.
-THHN/THWN-2 is rated for dry and damp locations, this should meet NEC requirements for wiring in outdoor NEMA 3R and NEMA 4 enclosures, correct?
-Will the distribution panel breaking out the 3P to the separate panels meet NEC if done with UL insulated mechanical lug / multitap wire connectors?
-Other than conduit what is a good way to bundle/group the THHN inside the house and provide strain relief at the enclosures clamps? Split wire loom?
-It shouldn’t matter what order I connect the 3P legs to the transformer on the primary or secondary, as I don’t care about the phasing, and any 2 legs will always be 120deg apart, correct?
-It shouldn’t matter which leg I ‘double tap’ and send to both panels, as all the legs ae equal in the MEP stator, correct?

Other gen NEC specific things I’m tracking:
-conductors must be rated at 115% of gen face plate (52x1.15=60A)
-over current protection on primary and secondary sides of transformer
-PVC conduit must be buried 18”, and conduit can only be 50% full by volume

Thanks all.

 

[Scoobyshep]

Transformer is a separately derived source and the neutral x0 must be bonded to ground. I believe the nec also requires a ground rod as well. I dont think the generator contactor counts as a disconnecting means as described in the nec definitions

 

[Tommytone]

After the good discussion in this thread I’ve revised my design a little bit. Below is the diagram of what I’m planning on doing. Welcome any comments and suggestions.

View attachment 886327

After the holidays I plan to start ordering the bits and get this install rolling before we have a serious outage and I have 15kWs sitting in the driveway I can’t use. Just last week there was a nasty car accident that took out a pole and the other side of the state road lost power for 18-24hrs overnight with temps in the low 20s.

I’ve also been reading the NEC some. My county has adopted NEC 2020, and while I haven’t decided if I’m pulling permits I do want to ensure that this install is fundamentally safe, and meets code. I have a few questions that I’m sure some of you will probably know the answers too. I’m also probably going to call the electrician that wired the house and pay him a few hours time to review this and do a walk through after I install.

Questions:
-with the 3P transformer is this still considered a non-SDS source? The GND is continuous across the system, but neutral now is not. The only earth ground is the service entry, and the only L0-GND bond is at the gen service terminals on the primary side and in the panels on the secondary side. To meet code would this need to be a SDS source and have a separate earth ground at the gen and break the ground at the transformer?
-I’ve fused L1/L2/L3 at 60A and running 6AWG THHN on the secondary side rated at 75A. Should I bump up the L0 conductor since many of the loads will be 120v loads using the neutral?
-NEC states that gens must be UL listed. Pretty sure MEPs are non-UL, can anybody confirm? This seems like an instant permit fail on a technicality.
-NEC requires a generator disconnect, does the MEP built in contactor meet this requirement? I included a fused disconnect incase it doesn't, and having it is probably a good idea anyways.
-THHN/THWN-2 is rated for dry and damp locations, this should meet NEC requirements for wiring in outdoor NEMA 3R and NEMA 4 enclosures, correct?
-Will the distribution panel breaking out the 3P to the separate panels meet NEC if done with UL insulated mechanical lug / multitap wire connectors?
-Other than conduit what is a good way to bundle/group the THHN inside the house and provide strain relief at the enclosures clamps? Split wire loom?
-It shouldn’t matter what order I connect the 3P legs to the transformer on the primary or secondary, as I don’t care about the phasing, and any 2 legs will always be 120deg apart, correct?
-It shouldn’t matter which leg I ‘double tap’ and send to both panels, as all the legs ae equal in the MEP stator, correct?

Other gen NEC specific things I’m tracking:
-conductors must be rated at 115% of gen face plate (52x1.15=60A)
-over current protection on primary and secondary sides of transformer
-PVC conduit must be buried 18”, and conduit can only be 50% full by volume

Thanks all.

Have you been able to complete the project with the transformer? I have been delayed but after getting my 805 running I am wondering how the transformer set up is working.

 

[Tommytone]

As I understand it, the issue isn’t so much heavy load as it is imbalance. Any load creates heat. The case on the main generator has to dissipate it. Loading one pair of legs and not the other creates hot sections on the main generator. This can lead to failure. Running a three phase generator as single phase causes the imbalance problem. I had similar concerns because of my use case. I incorporated a three phase transformer to deal with it. This way, I’m transferring the unbalanced load to the transformer, which is a chunkier piece of steel. It can handle heat much better and arguably it’s cheaper to replace, a very unlikely occurrence.

Is your transformer inside or Outside? Are you running 208 to the transformer or are you running higher volts and stepping down?

 

[MDdeuce]

Have you been able to complete the project with the transformer? I have been delayed but after getting my 805 running I am wondering how the transformer set up is working.

No, with holidays and such I haven't done much of anything. I'm hoping to get parts ordered in the near-ish future and get things going. Once I get it done I'll post pics.

 

[Tommytone]

No, with holidays and such I haven't done much of anything. I'm hoping to get parts ordered in the near-ish future and get things going. Once I get it done I'll post pics.

Couple questions if I can. Will the transformer be inside? Most Of the transformers I am seeing are 480v by 208 v but that is different than what you are using correct?

 

[MDdeuce]

Couple questions if I can. Will the transformer be inside? Most Of the transformers I am seeing are 480v by 208 v but that is different than what you are using correct?

I'm putting the transformer outside, which will make my install simpler for several reasons, but also largely because I have no easy way to get the 500lbs transformer into the basement. I need to make rain hoods for it so it will be nema 3r.

I was looking for a 30kva delta-wye 208/120, but I couldn't find any locally, I was able to find a 63kva delta-wye 460/266. As the winding ratios are the same it will largely work the same at 208v as the nameplate 460. A 480/208 has different winding ratios, so if you run the primary delta at 208 your neutral will be low, more like 90v rather than 120v.

Also keep in mind that on the higher voltage units the rated current will be less that a similar rated 208v unit as the higher voltage (that you're not using) eats up the kva raining. Even though my unit is rated at 63kva it's only good for 79A/leg. This is still plenty for a MEP-804B, but probably less that one would expect for 63kva.

 

[MDdeuce]

I also like the safety/fire aspects of the used transformer being outside. It being outside also makes NEC compliance easier.

Also make sure you are getting a dry type transformer. I think most in this kva rating are dry type. The oil filled ones are a potential nightmare if it leaks.

 

[Evvy Fesler]

Have you been able to complete the project with the transformer? I have been delayed but after getting my 805 running I am wondering how the transformer set up is working.

Hi - sorry about the delayed response. I've been very busy. No, not yet. Please don't laugh at me, but it's cold here and so this project is on hold until spring. I know... North Carolina is cold, right?..!!!

 

[Evvy Fesler]

Is your transformer inside or Outside? Are you running 208 to the transformer or are you running higher volts and stepping down?

The one that I bought is isn't housed for outside so I'll put it under cover; probably in the barn. It will need ventilation.... nothing fancy, but a small room would get warm.