Wiring up a 30HP rotary phase converter

[ronsii]

You shouldn't be fused at 200 amps if your incoming is 1/0 AL.

The electrician was saving money that day

[Oscar]

If primary voltage is underground you have on the ground box transformers. These will typically be spaced 625' apart, or closer so each house will have 400' or less secondary voltage service cable. In a development they might place them at lot lines along the street, or behind houses where they easily supply 4 houses if homes are back to back.

It's a gamble to contact the power company, they might be helpful, or might start quoting fine print & deny you the privilege of heavy machines or welders.

An inverter welder isn't going to cause much alarm like air arcing with a 400 amp transformer. A BIG phase converter might. Then your option might be a soft start.

behind my house is a park, and there are no transformers that I can see there. It must be located in one of the neighbor's yards then?

I agree, with what you said about the power company. I don't know how picky they will be and if they will start asking too many questions, lol.

You shouldn't be fused at 200 amps if your incoming is 1/0 AL.

See that's the thing, for some odd reason, when this house was built in the early 90's, the electrician did not put a true "main panel" outside; I called it that because it is the one outside getting the power from the power meter. The electrician installed what appears to me as a sub-panel, because it has no main breaker to indicate the service ampacity coming into the house. It is connected directly to the power meter next to it. That outside sub-panel then powers (by way of four 240V spaces) the AC, Stove, my Air compressor, and the Garage sub-panel which then powers the rest of the house. I thought it was very odd, but it must have passed inspection several times as I'm not the first owner of this house, I'm the 3rd. So because of that, I don't know what the service ampacity is. Therein lies the conundrum. Like ronsii said, the electrician was saving money that day and probably just slapped in whatever he had, lol.

One thing that I'm highly considering is adding more starting caps. The ones in my RPC panel are 270μF ea, and there are 10 of them. I can easily get 10 more on Ebay for $80.

scsmith, how many starting caps are you running on your 30HP RPC?

[ronsii]

But won't increasing the starting capacitance also increase the initial surge draw?

[Oscar]

But won't increasing the starting capacitance also increase the initial surge draw?

To me that wouldn't make sense because then they wouldn't be helping anything out and would then technically serve no purpose. If I'm not mistaken, the capacitors charge up when power is provided to the panel (aka when the breaker for the panel is switched-on). That way when the On button is pressed, they are ready to discharge to provide power to the motor to assist in "taking off". Someone correct me if I'm wrong here.

Or, perhaps they charge up first via the timer, which would then disconnect them after they discharge also via the timer, and then the main single-phase power takes over? I this is the case , then it seems there would be an initial surge that charges up the caps first (before the motor comes online), but that energy stored in the caps is very little. Less than 1 Joule per cap.

[ronsii]

Here's a sat view and street view of a development we did a couple years ago, primary heat and cooking was gas so they put 14 residences on one transformer... I drew the red secondary lines from memory... so might be off a bit here an there also water and gas pretty much followed the power.

The Transformer is in the bottom center of the pic... red/green arrow pointing to it.


Here is the street view of it... transformer is in the bushes with the green arrow pointing down at it.

[ronsii]

Also notice how the power lines run ~4 feet behind the sidewalk, this is pretty standard for residential around here.

[Oscar]

Also notice how the power lines run ~4 feet behind the sidewalk, this is pretty standard for residential around here.

I see. I never bother to look around the front. My neighborhood is kinda like that cul-de-sac, except the cul-de-sac is a city park, and the rear of the houses are the perimeter of the park.

So I just opened the gate at the back of my yard that leads to the park. Two houses down, they have a wire fence and I spotted a cubic box about 30", in the corner of the rear of the yard.



So, no way I can get to it to check it out. I don't know those neighbors.

[ronsii]

Here is a pic when we were doing the last couple of homes in that same development. you can just see the transformer in the left side of the pic... the bushes have since grown up!!



Here is the house in the back righthand corner of the dev, power,water,gas trench went under the driveway as they 'flipped the house design after the plat was designed otherwise the secondaries would have been within 20-30 feet of the panel entrance... a straight shot... they do this a lot when people are looking at the plans of the house they want to build... and decide they like it better flipped most all of the entrance panels on these houses were in the garages you can see it in the pic.


And here is how we put the conduit coming out of the bottom of the panel in the garage right through the concrete footings and 90 out the the front and about 3 + feet depth. gas and water will shoot passed the power line and continue towards the back of the house another 5-10 feet for the gas line and then another 10-20 foot for the water.

[Oscar]

Would have been awesome if the transformer was in my backyard. I'd have beefed up the wiring in no time flat!

[ronsii]

Would have been awesome if the transformer was in my backyard. I'd have beefed up the wiring in no time flat!

So.... your power meter is on the back of your house???

[scsmith42]

You must know where your utility transformer is. If it is ground mounted, it may have an attached nameplate supplying capacity info.

Do you share with other residential customers?

Do you have neighbors you feel confident asking if they have trouble.

It may be fine. Three seconds after start up it will be fine. It MAY knock out your neighbor's TV, or they may be fine. Several variables are still unknown. Try it, see what happens.

Bill, in my instance only my shop and the house my mother in law lives in is on that particular transformer. As I recall the overhead service coming in from the utility is only #4 or #2. They seem to have their own rules regarding wire sizing to the meter.

[Oscar]

So.... your power meter is on the back of your house???

nah, the power meter is on the side of the house, the side adjacent to my neighbor that has the swimming pool.

[Willie B]

Bill, in my instance only my shop and the house my mother in law lives in is on that particular transformer. As I recall the overhead service coming in from the utility is only #4 or #2. They seem to have their own rules regarding wire sizing to the meter.

Corporations, if large (powerful) enough are exempt from the laws of physics.

My utility talks of voltage drop in underground (customer owned) services. Verbal sleight of hand, they only discuss ampacity in overhead drops (utility owned).

It might be common to have a 200 amp service on a house, it is often fed with a #4 aluminum drop. They are exempt from NEC. They argue that if the #4 ever burns off, they will upgrade it.

Meanwhile, power quality might be awful because voltage fluctuates with load.

The formula they force on owners & their electricians is KIL2/Ed. This gives a CMA (Circular Mil Area. K factor is resistance per mil foot. I is amperage. L is distance conductor length. 2, because it travels round trip. Ed is acceptable loss. Green Mountain Power imposes an acceptable loss at 1% if the customer is paying. I (amperage) is based on the breaker size.

When they provide an overhead service, they factor transformer rating. A 15 KW transformer works out to 62.5 amps. Loss, if GMP pays for cable, is factored at 3%

They still violate code rules as for temperature at terminations, but code does not apply to utilities.

[Willie B]

Code until now allowed up to 6 disconnects per service. They can be outside or in, but if indoor, cable length is severely limited. 2020 edition of NEC calls for a single service disconnect ahead of your four breakers. In your case, the one outside is the service disconnect. Everything downstream is feeders & sub panels.

[William McCormick]

While I use Temflex 1700, I urge you to consider the rubber splicing tape as a filler. You want enough 3M 33+ to do the job. Split bolts, especially if you get too large have a lot of knobby points that compress the rubber splicing tape. It is common for it to chafe through. I've also seen the rubber stuff split wide open when it gets old. It sometimes makes a wild fireworks show.

In this application I'd leave the Temflex 1700 in the drawer, and use 33+ with Scotchfill, then another heavy layer of 33+. My father then used friction tape, a heavy tarry cloth tape.

The conductors you are working with aren't very stiff, but trough work where heavy conductors (500 MCM) are tapped you need all the protection you can get.

When I do split bolts I use rubber tape, then friction tape, then electrical tape. You can take a razor knife and jab it as hard as you can and it will not make it through, that friction tape is tuff stuff.




Sincerely,

William McCormick

[William McCormick]

Bill, in my instance only my shop and the house my mother in law lives in is on that particular transformer. As I recall the overhead service coming in from the utility is only #4 or #2. They seem to have their own rules regarding wire sizing to the meter.

There is no current limiting device after the transformer so the drop from the pole can carry high amperage all day long with no voltage drop. That same size wire after two circuit breakers cannot carry high amperage.

Sincerely,

William McCormick

[Oscar]

Thanks for the input everyone. Just finished mounting the electrical boxes to the rolling cart. I didn't wanna tear up the walls for this, and plus I sometimes dont like things being too permanent, so its like a little rolling power station I can move around the garage. I should have it wired and running this weekend.

[William McCormick]

Corporations, if large (powerful) enough are exempt from the laws of physics.

My utility talks of voltage drop in underground (customer owned) services. Verbal sleight of hand, they only discuss ampacity in overhead drops (utility owned).

It might be common to have a 200 amp service on a house, it is often fed with a #4 aluminum drop. They are exempt from NEC. They argue that if the #4 ever burns off, they will upgrade it.

Meanwhile, power quality might be awful because voltage fluctuates with load.

The formula they force on owners & their electricians is KIL2/Ed. This gives a CMA (Circular Mil Area. K factor is resistance per mil foot. I is amperage. L is distance conductor length. 2, because it travels round trip. Ed is acceptable loss. Green Mountain Power imposes an acceptable loss at 1% if the customer is paying. I (amperage) is based on the breaker size.

When they provide an overhead service, they factor transformer rating. A 15 KW transformer works out to 62.5 amps. Loss, if GMP pays for cable, is factored at 3%

They still violate code rules as for temperature at terminations, but code does not apply to utilities.

A single conductor aluminum wire 100 feet long #2 AWG will lose 2.61 volts drawing 100 amps on one leg, a number four would lose 4.16 volts doing the same.

That is why I put in 4/0 or 0000 copper wire in my son's house for a 200-amp service, which will cause a 0.66-volt drop at 200-amps. The wire feeding the house looked like 1/0 aluminum and will create a voltage drop of 4.950-volts at 200-amps over the 75-foot run to the mast. The house has two hot legs and in theory, that can supply 400-amps of 120-volt power or 200-amps of 240-volt power. Which I do not think he will use, haha. The two heat pumps run on 240 volts and have an RLA (Run Load Amps) under ten amps in the hi-stage. The electric strip heaters run on 240 volts and take 33 amps each and there are two sets but only run when it is below 25 degrees outdoor temp, which is monitored by the ecobee thermostats in conjunction with local weather. There is a hot water heater, an electric range, and all lights are super low wattage LEDs. He is working on the jacuzzi which is already wired up to where it goes, with a 50 amp ground fault breaker feeding it. But I suspect it will not take near 50 amps.

But when you have two phases some of the power supplying 240 and some supplying 120 you really have three wires carrying power. So I think all those numbers would actually be proven a bit high in actual practice unless you are drawing 200 amps at 240 volts.


Sincerely,

William McCormick

[Willie B]

A single conductor aluminum wire 100 feet long #2 AWG will lose 2.61 volts drawing 100 amps on one leg, a number four would lose 4.16 volts doing the same.

That is why I put in 4/0 or 0000 copper wire in my son's house for a 200-amp service, which will cause a 0.66-volt drop at 200-amps. The wire feeding the house looked like 1/0 aluminum and will create a voltage drop of 4.950-volts at 200-amps over the 75-foot run to the mast. The house has two hot legs and in theory, that can supply 400-amps of 120-volt power or 200-amps of 240-volt power. Which I do not think he will use, haha. The two heat pumps run on 240 volts and have an RLA (Run Load Amps) under ten amps in the hi-stage. The electric strip heaters run on 240 volts and take 33 amps each and there are two sets but only run when it is below 25 degrees outdoor temp, which is monitored by the ecobee thermostats in conjunction with local weather. There is a hot water heater, an electric range, and all lights are super low wattage LEDs. He is working on the jacuzzi which is already wired up to where it goes, with a 50 amp ground fault breaker feeding it. But I suspect it will not take near 50 amps.

But when you have two phases some of the power supplying 240 and some supplying 120 you really have three wires carrying power. So I think all those numbers would actually be proven a bit high in actual practice unless you are drawing 200 amps at 240 volts.


Sincerely,

William McCormick

1 phase.

At 240 volts it requires 2 conductors to deliver 1 phase to your house. We cut that one phase in half to get 120 Volt power. If the 2 halves of the 1 phase source are in balance, the center tap conductor carries no load.

You are correct voltage loss is greatest at peak load, so any time any conductor carries less load, it loses less voltage.

[Oscar]

I'd like to thank everyone that contributed to this long-winded thread.






With 2/0 copper wire feeding the juice within 2-feet of the RPC panel (all the way from the house main panel), the lights didn't even dim! My 10HP compressor has more in-rush!

[filetobeef]

@Oscar.
can you recap the wiring and breaker arrangement? need to install my 30hp rpc also.

[Oscar]

@Oscar.
can you recap the wiring and breaker arrangement? need to install my 30hp rpc also.

Yes, I will describe it, but no pics because it's not exactly up to code

This list goes in order sequentially where the line you are reading feeds the item directly below it

Main Panel outside w/ 125A Eaton BR2125
2/0 copper wire, 15ft
Garage Subpanel/loadcenter w/ 125A Eaton BR2125
2/0 copper wire (hots) + 4awg ground + 6awg neutral (straight to load center below), 50ft,
1-Φ 240V single-Breaker box w/ 125A Eaton BR2125 (this is my "disconnect")
1awg copper wire + 4awg ground, 9"
1-Φ 240V load center w/100A Eaton BR2100
2awg copper wire x 2 + 8awg ground, 24"
RPC Panel main contactor***
4awg copper wire x 3 + 8awg ground, 30"
Rotary Phase Converter (North American Electric PC286T‐30‐4 induction motor, TECF)
***=Main contactor T1-T2-T3 that connects to motor, also has 6awg x 3 going into the 3-Φ breaker, 40A Eaton BR340
6awg x 3, 8awg ground, 10"
14-50R receptacle for three hots + 1 ground
welder



with all the oversized wire, it paid off because between that and the 10 motor starting-capacitors, I can barely even see the lights dim when I turn it on! I haven't measured it, but I'm pretty sure there is only 4V or maybe 5V drop. My 10HP air compressor with it's single phase 240V motor draws more in-rush! It definitely causes a flicker, but the RPC hardly.

[filetobeef]

@ Oscar
thanks for the info.
did you try welding to full capacity yet to see what the rpc really handles? noise when it loads up? voltage stability etc...?

[Oscar]

Not yet, but soon will.

[ronsii]

Yes, I will describe it, but no pics because it's not exactly up to code

This list goes in order sequentially where the line you are reading feeds the item directly below it

Main Panel outside w/ 125A Eaton BR2125
2/0 copper wire, 15ft
Garage Subpanel/loadcenter w/ 125A Eaton BR2125
2/0 copper wire (hots) + 4awg ground + 6awg neutral (straight to load center below), 50ft,
1-Φ 240V single-Breaker box w/ 125A Eaton BR2125 (this is my "disconnect")
1awg copper wire + 4awg ground, 9"
1-Φ 240V load center w/100A Eaton BR2100
2awg copper wire x 2 + 8awg ground, 24"
RPC Panel main contactor***
4awg copper wire x 3 + 8awg ground, 30"
Rotary Phase Converter (North American Electric PC286T‐30‐4 induction motor, TECF)
***=Main contactor T1-T2-T3 that connects to motor, also has 6awg x 3 going into the 3-Φ breaker, 40A Eaton BR340
6awg x 3, 8awg ground, 10"
14-50R receptacle for three hots + 1 ground
welder



with all the oversized wire, it paid off because between that and the 10 motor starting-capacitors, I can barely even see the lights dim when I turn it on! I haven't measured it, but I'm pretty sure there is only 4V or maybe 5V drop. My 10HP air compressor with it's single phase 240V motor draws more in-rush! It definitely causes a flicker, but the RPC hardly.

LOL!!!! sounds like you're afraid of the code nazi's on here..

Glad to hear it's working good!!! I always shied away from a big RPC just because of the inrush draw as we are on a shared transformer with not the best starting voltage to begin with... but sounds like I probably worried too much and ought to just do it as I have a 20hp on my big 30 inch lathe and you have to run a genny to use it right now...