Rotory Phase Converter

[Jkr3497]

I have a phase converter I have installed. Per the manufactures installation manual the rotor will produce up to 150 amps. The manual says to feed the unit with 1 phase 225 amps. I am doing so with a 4/0 cu thhn. It says the 3phase output should be a 1/0. what is protecting the 1/0 if I am feeding the whole setup with 225amps? I am feeding a main lug 3 phase panel. My inspector stopped and looked at it, he says I need a 150 main breaker in the panel. Is he right or do I have an argument? In my eyes I am feeding the whole setup with the 250% it should have.

:?

 

[texie]

The inspector is wrong. If you have 150 amps @240, 3 phase on the secondary that is roughly 60 KVA. Well, you have to input at least 60 KVA of power so that would be about 250 amps @240 1 phase. That unit should have a built in motor starter to protect the generator and you should have a main breaker on the 3 phase side.
As a side note, that ground bar is not compliant. That needs to be a 1/4 X 2 busbar.

Edit to add....is that enclosed breaker I see at the left the output 3 phase main breaker?

 

[Jkr3497]

The enclosed breaker on the left is a 225 single phase. The three phase panel is in the middle. 150 main lug. Why do you say the ground bus bar is incorrect? Why would I have to have a main breaker in the panel.

 

[kwired]

The inspector is wrong. If you have 150 amps @240, 3 phase on the secondary that is roughly 60 KVA. Well, you have to input at least 60 KVA of power so that would be about 250 amps @240 1 phase. That unit should have a built in motor starter to protect the generator and you should have a main breaker on the 3 phase side.
As a side note, that ground bar is not compliant. That needs to be a 1/4 X 2 busbar.

Edit to add....is that enclosed breaker I see at the left the output 3 phase main breaker?

It is not a motor it is a phase converter. Art 430 doesn't apply to it. Art 455 applies and overcurrent protection should be no more then 125% of the input current rating.

It will need reduced overcurrent protection on the output side.


Jkr3497, think of it this way:

Full VA of the input is only on two leads, current will be higher then the same VA of output split through three leads. And any internal losses will be added to what is input as well.


I will not say that the output of this is as perfectly balanced as a true three phase system, the "manufactured" phase will not be a steady voltage at all times and will vary much more then the other two lines when there are load changes, and current in connected motors is never balanced like it is from a true three phase system. It is probably a good idea to not supply motors that run at rated HP, at least for extended periods of time anyway with such a supply.

They are popular here for center pivot irrigation where three phase supply isn't easily available, but the nature of loads on those is a cycle of a few seconds to a minute or so and not continuous loading, and you need to make sure the control transformer for the machine is not connected to the "manufactured" phase or it will not get a steady 480 volts nominal input.

 

[kwired]

The enclosed breaker on the left is a 225 single phase. The three phase panel is in the middle. 150 main lug. Why do you say the ground bus bar is incorrect? Why would I have to have a main breaker in the panel.

You need a 150 amp overcurrent device in the output of the converter - could be a main breaker in your panel.

What is in the black box that goes with the converter? My guess is mostly just capacitors.

 

[texie]

The enclosed breaker on the left is a 225 single phase. The three phase panel is in the middle. 150 main lug. Why do you say the ground bus bar is incorrect? Why would I have to have a main breaker in the panel.

250.64(D)(3) for the ground bar. This was rewritten starting with the 2008 NEC (I think 2008) to prevent just what you used. The bar must be 1/4" X 2 busbar.
The panelboard must be protected at its ampacity. See 408.36. Also the conductors must be protected per Art. 240.
Take a look at Article 455 for some of the requirements regarding OCPDs and currents for phase converters.
In any event, the inspector is wrong on the input breaker as it obviously has to be bigger that the output to get the same KVA.

 

[jap]

250.64(D)(3) for the ground bar. This was rewritten starting with the 2008 NEC (I think 2008) to prevent just what you used. The bar must be 1/4" X 2 busbar.
The panelboard must be protected at its ampacity. See 408.36. Also the conductors must be protected per Art. 240.
Take a look at Article 455 for some of the requirements regarding OCPDs and currents for phase converters.
In any event, the inspector is wrong on the input breaker as it obviously has to be bigger that the output to get the same KVA.

If the Inspector was talking about needing a 150 Amp Breaker in the panel that the Phase converter was feeding, then I'd say the Inspector was right not wrong.

JAP>

 

[kwired]

250.64(D)(3) for the ground bar. This was rewritten starting with the 2008 NEC (I think 2008) to prevent just what you used. The bar must be 1/4" X 2 busbar.
The panelboard must be protected at its ampacity. See 408.36. Also the conductors must be protected per Art. 240.
Take a look at Article 455 for some of the requirements regarding OCPDs and currents for phase converters.
In any event, the inspector is wrong on the input breaker as it obviously has to be bigger that the output to get the same KVA.

250.64(D)(1)(3) in the 2014 NEC anyway. I don't think it prohibits a listed assembly, it is just a requirement that a simple bar be 1/4 x 2 inch copper, connections to that bar must be exothermic welded or listed connectors. What the OP has used has connectors already built into it, but would need to meet part (2) instead of (3) which says it must be listed as grounding and bonding equipment. If anything he has a violation of part (2) instead of (3) as I see it.

 

[texie]

If the Inspector was talking about needing a 150 Amp Breaker in the panel that the Phase converter was feeding, then I'd say the Inspector was right not wrong.

JAP>

Maybe I misunderstood the OP. I thought he was saying he needed a 150 amp input breaker as opposed to the 225 that he has. But yes, I think it needs a 150 breaker on the output side, which I stated.

 

[augie47]

250.64(D)(3) for the ground bar. This was rewritten starting with the 2008 NEC (I think 2008) to prevent just what you used. The bar must be 1/4" X 2 busbar.
.

Not doubting you, but I don't see that (yet) , at least in the '08 or '11. I see the need for a "listed" connector, but not for a buss bar. Can you direct me to the requirement ?

 

[texie]

250.64(D)(1)(3) in the 2014 NEC anyway. I don't think it prohibits a listed assembly, it is just a requirement that a simple bar be 1/4 x 2 inch copper, connections to that bar must be exothermic welded or listed connectors. What the OP has used has connectors already built into it, but would need to meet part (2) instead of (3) which says it must be listed as grounding and bonding equipment. If anything he has a violation of part (2) instead of (3) as I see it.

As I mentioned this wording was changed in 2008. It changed again in the 2014 in an attempt to prevent what the OP used. Under the old wording he probably has a bar that is at least 1/4" X 2 on 2 dimensions. That is not what the NEC intended. It must be 1/4" X 2" X whatever length is needed for all connections, hence the rewording. The busbar does not have to be listed, rather the connectors attaching the GECs or jumpers.

 

[augie47]

250.64(D)(3) Common Location.

A grounding electrode conductor shall be connected to the grounded service conductor(s) in a wireway or other accessible enclosure on the supply side

of the service disconnecting means. The connection shall be made with exothermic welding or a connector listed as grounding and bonding equipment. The grounding elec-trode conductor shall be sized in accordance with 250.66 based on the service-entrance conductor(s) at the common location where the connections are made.


I don't see the buss bar requirement !

 

[texie]

It is not a motor it is a phase converter. Art 430 doesn't apply to it. Art 455 applies and overcurrent protection should be no more then 125% of the input current rating.

It will need reduced overcurrent protection on the output side.


Jkr3497, think of it this way:

Full VA of the input is only on two leads, current will be higher then the same VA of output split through three leads. And any internal losses will be added to what is input as well.


I will not say that the output of this is as perfectly balanced as a true three phase system, the "manufactured" phase will not be a steady voltage at all times and will vary much more then the other two lines when there are load changes, and current in connected motors is never balanced like it is from a true three phase system. It is probably a good idea to not supply motors that run at rated HP, at least for extended periods of time anyway with such a supply.

They are popular here for center pivot irrigation where three phase supply isn't easily available, but the nature of loads on those is a cycle of a few seconds to a minute or so and not continuous loading, and you need to make sure the control transformer for the machine is not connected to the "manufactured" phase or it will not get a steady 480 volts nominal input.

I was not implying that this is an Art. 430 application. I was thinking of a single motor on the load side where some manufacturers offer a built in motor starter for this. But then I realized that he is feeding a panelboard with multiple loads. As mentioned, I may have misread the OP details on a couple of fronts.
Otherwise I think we agree that he needs to protect the output conductors and the panelboard.

 

[texie]

250.64(D)(3) Common Location.

A grounding electrode conductor shall be connected to the grounded service conductor(s) in a wireway or other accessible enclosure on the supply side

of the service disconnecting means. The connection shall be made with exothermic welding or a connector listed as grounding and bonding equipment. The grounding elec-trode conductor shall be sized in accordance with 250.66 based on the service-entrance conductor(s) at the common location where the connections are made.


I don't see the buss bar requirement !

Sorry typo in my reference. Should be 250.64(D)(1)(3).

 

[kwired]

Not doubting you, but I don't see that (yet) , at least in the '08 or '11. I see the need for a "listed" connector, but not for a buss bar. Can you direct me to the requirement ?

He gave the wrong section but was close, in 2014 anyway it is 250.64(D)(1)(3), instead of (D)(3).

As I mentioned this wording was changed in 2008. It changed again in the 2014 in an attempt to prevent what the OP used. Under the old wording he probably has a bar that is at least 1/4" X 2 on 2 dimensions. That is not what the NEC intended. It must be 1/4" X 2" X whatever length is needed for all connections, hence the rewording. The busbar does not have to be listed, rather the connectors attaching the GECs or jumpers.

My argument (based on what I read in 2014) is that he doesn't have what is being referred to in part (3) so it doesn't apply.
He may have a violation of what is required by part (2) though - depends on if what he has is listed a grounding and bonding equipment.

Chances are if it were listed as such it would probably be bronze, but that it just a somewhat educated guess, and it wouldn't be bronze if listed for aluminum conductors so the bronze theory is not necessarily automatic either.

 

[iwire]

Guys, I must be missing something.

If you add a phase, the available output current must decrease. If they tried to pull more than 150 amps from the output I would expect the 225 amp input breaker to open.

You can't output more kva than you put in.

I suspect the manufacturer is correct.

 

[augie47]

I would tend to agree. Without additional information one could not confirm that the connection shown is "listed as grounding or bonding equipment"... my guess would be that it is but that is an unqualified assumption.
I see similar installs often where the electrician uses neutral/grounding bars such as the ones in panelboard cabinets.
I may be making a mistake, but if it's good enough for panelboard neutral./grounding connections, I tend to approve it.

 

[kwired]

Guys, I must be missing something.

If you add a phase, the available output current must decrease. If they tried to pull more than 150 amps from the output I would expect the 225 amp input breaker to open.

You can't output more kva than you put in.

I suspect the manufacturer is correct.

You must be missing something.

I think that is what most of us have been trying to say, but maybe in a different way.

 

[iwire]

You must be missing something.

I think that is what most of us have been trying to say, but maybe in a different way.

No, we are not saying the same thing.

You guys seem to be saying that a 150 amp OCPD must be added in the output wiring.

I am saying the 225 on the input side provides that protection.

 

[kwired]

No, we are not saying the same thing.

You guys seem to be saying that a 150 amp OCPD must be added in the output wiring.

I am saying the 225 on the input side provides that protection.

Correct. but the output conductors need 150 amp OCPD if they are going to be 150 amp conductors. The point of reduction to that OCD is a feeder tap. Two lines are effectively direct connected to the input in such a converter, so at very least you have on those two lines the equivalent of a 150 amp conductor directly tapped to one with 225 amps overcurrent protection. The "manufactured" phase may be somewhat inherently protected from overload just by the impedance of the converter - but NEC likely wouldn't recognize that as proper protection anyway.