Delta High Leg with Control Wire Question

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Electricalhelp

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I need you to assist here in verifying all your 3 phase kitchen equipment, which supply power from A panel to be powered by a 120/240V delta high leg C phase electrical service. They cannot have controls powered by C phase which is the high leg and meters 240V from phase to ground.
This needs to be confirmed for any single phase or 3 phase piece of equipment powered out of the 3phase 600amp panel A with Delta High Leg on C.

How do I know if an equipment has an control wiring?
Since the equipment cut sheet calls out for a 240V/3P or 240/1P

If there is equipment under the hood and requires a shut trip breaker, should I just make the whole Panel a Shut Trip Panel instead
 
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The code requires the high leg to be B phase but many utilities require it to be in the C phase position for their metering so you will need to verify that.
As far as any controls, those will be an issue if they are 120 volt line to neutral controls. You will either have to look at the schematics for the equipment or ask the manufacturer.
 
don_resqcapt19 said:
The code requires the high leg to be B phase but many utilities require it to be in the C phase position for their metering so you will need to verify that.
As far as any controls, those will be an issue if they are 120 volt line to neutral controls. You will either have to look at the schematics for the equipment or ask the manufacturer.
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I confirm with the utility company and they said it was Phase C

Do you have an example of 120V line to neutral controls? How would the system work with a Delta High Leg?

I only have access to the electrical equipment cuts from the manufacturer.

Why did the Project Manager say something about the 240V/3P and 240/1P equipment with controls will be a issue with the Delta High Leg.
 
As don mentioned, for the utility wiring (meter) it is "C" phase but the NEC requires premises wiring to use "B" as the "High-Leg". That said, you need to check the individual panel in question as some are wired with High-Leg on "C".

To prevent burning up equipment you need to follow don's direction and check the equipment schematic or specifics from the manufacturer but if the nameplate states 240/3P or 240/1P without mention of 120v, there is a distinct possibility it doesn't need a neutral so the high leg won't matter but better safe than sorry.
 
augie47 said:
As don mentioned, for the utility wiring (meter) it is "C" phase but the NEC requires premises wiring to use "B" as the "High-Leg". That said, you need to check the individual panel in question as some are wired with High-Leg on "C".

To prevent burning up equipment you need to follow don's direction and check the equipment schematic or specifics from the manufacturer but if the nameplate states 240/3P or 240/1P without mention of 120v, there is a distinct possibility it doesn't need a neutral so the high leg won't matter but better safe than sorry.
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Also don't forget the single phase loads that have L-G connected electronics, filters or capacitors, like some VFDs.
 
augie47 said:
As don mentioned, for the utility wiring (meter) it is "C" phase but the NEC requires premises wiring to use "B" as the "High-Leg". That said, you need to check the individual panel in question as some are wired with High-Leg on "C".

To prevent burning up equipment you need to follow don's direction and check the equipment schematic or specifics from the manufacturer but if the nameplate states 240/3P or 240/1P without mention of 120v, there is a distinct possibility it doesn't need a neutral so the high leg won't matter but better safe than sorry.
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So if the equipment calls out for an additional 120V/1P outlet for an equipment with 240/3P or 240/1P power requirement, I just need to rearrange my Panel Schedule so no loads are connected to Phase C for the 120V/1P control wire
 
Electricalhelp said:
So if the equipment calls out for an additional 120V/1P outlet for an equipment with 240/3P or 240/1P power requirement, I just need to rearrange my Panel Schedule so no loads are connected to Phase C for the 120V/1P control wire
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Assuming phase C is the high leg, yes. As others have said, this is no longer the standard, since B-phase is the modern standard for the high leg, though some utilities may have legacy standards for their meter socket.

All of your 1-pole circuits need to avoid the high leg. A good practice is to set up a single phase subpanel for all the 1-pole circuits, and connect it to the two non-high-legs, and the neutral. This avoids the issue of someone in the future, trying to use a vacant space that they can't use.

The high leg can be used for inter-phase loads (i.e. 240V not requiring neutral), and 3-phase loads, provided you have straight-rated breakers instead of slash ratings (i.e. look for "240V" as opposed to "120/240V"). Given a 3-phase load with built-in control circuits strictly requiring 120V, make sure you arrange the phases so the one (or ones) that host 120V circuits, are not on the high leg phase. If I were a manufacturer anticipating this issue, I'd use the A-phase for control circuits, so it could work for either standard.
 
Carultch said:
Assuming phase C is the high leg, yes. As others have said, this is no longer the standard, since B-phase is the modern standard for the high leg, though some utilities may have legacy standards for their meter socket.

All of your 1-pole circuits need to avoid the high leg. A good practice is to set up a single phase subpanel for all the 1-pole circuits, and connect it to the two non-high-legs, and the neutral. This avoids the issue of someone in the future, trying to use a vacant space that they can't use.

The high leg can be used for inter-phase loads (i.e. 240V not requiring neutral), and 3-phase loads, provided you have straight-rated breakers instead of slash ratings (i.e. look for "240V" as opposed to "120/240V"). Given a 3-phase load with built-in control circuits strictly requiring 120V, make sure you arrange the phases so the one (or ones) that host 120V circuits, are not on the high leg phase. If I were a manufacturer anticipating this issue, I'd use the A-phase for control circuits, so it could work for either standard.
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All my 1 Pole circuits are on a single phase subpanels already.

Based on the cut sheets from the franchise, I would have to assume there is no control wiring for the equipment if it only mentioned either 240V/3P or 240/1P connection requirement for the partial equipment in questions.

But for example, if the Fryer calls out for a 240V/3P/30AMP breaker. I assumed it is okay to connect to the delta high leg since they did not mention an additional control wiring.

How would I show the shut trip breaker for the equipment
 
If your machines have control circuits supplied directly from the input and has 120 volt components, you need to pay close attention so you don't get said control circuits on the high leg.

If your machines have a control transformer that has input tied line to line to the transformer primary - you don't have to be concerned other than if there is other voltage taps for the transformer primary (maybe it has a 208 and a 240 input tap and you need to select which one applies to your supply).

If the main supply terminals doesn't have a neutral position, chances are you are ok with a high leg in any position in the supply circuit presuming 240 volts is an acceptable input voltage.
 
Electricalhelp said:
All my 1 Pole circuits are on a single phase subpanels already.

Based on the cut sheets from the franchise, I would have to assume there is no control wiring for the equipment if it only mentioned either 240V/3P or 240/1P connection requirement for the partial equipment in questions.

But for example, if the Fryer calls out for a 240V/3P/30AMP breaker. I assumed it is okay to connect to the delta high leg since they did not mention an additional control wiring.

How would I show the shut trip breaker for the equipment
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Assuming P stands for phase (as opposed to pole), 240V/1P loads can be connected either be connected across the standard legs, or from high leg to standard leg, as long as it doesn't "care" where the neutral is, relative to its supply terminal voltages. You'd need a 2-pole straight rated breaker for this application, if one of the poles is the high leg. These are common of 2-pole breakers for the 240V & 208V application, but you have to check the breaker datasheet to confirm it doesn't state "120/240V".

To show a shunt trip, I recommend drawing a bordered text field with the words "SHUNT TRIP" inside it, adjacent to your breaker symbol, opposite the notation of its trip and pole spec. Then draw another auxiliary circuit line with an arrow pointing to it, to indicate where the control and power for the shunt trip circuit comes from.
 
Electricalhelp said:
I confirm with the utility company and they said it was Phase C

Do you have an example of 120V line to neutral controls? How would the system work with a Delta High Leg?

I only have access to the electrical equipment cuts from the manufacturer.

Why did the Project Manager say something about the 240V/3P and 240/1P equipment with controls will be a issue with the Delta High Leg.
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But if the electrician did the service installation correctly, it will be B phase in the service and other interior panels.
He said that because if the controls are 120 volt, and connected line to neutral, and the ungrounded conductor that the controls are connected to, will be 208 volts line to neural
 
don_resqcapt19 said:
But if the electrician did the service installation correctly, it will be B phase in the service and other interior panels.
He said that because if the controls are 120 volt, and connected line to neutral, and the ungrounded conductor that the controls are connected to, will be 208 volts line to neural
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If the panel has several single pole or even double pole breakers in it, every third space that is not used is going to be the high leg regardless if it is in compliance with code or not ;)
 
kwired said:
If the panel has several single pole or even double pole breakers in it, every third space that is not used is going to be the high leg regardless if it is in compliance with code or not ;)
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Yes, but I did not see anything from the OP that said that.
 
Is this a decent explanation to explain for someone to understand

You can connect the equipment to a 3 Phase Breaker
But internally we do not know how the control circuit is wired.
The equipment internally can be Connected to Phase A and B to run the equipment and then Phase C is the control wiring. If this is the case, then the equipment will not work.
But if the equipment internally can be Connected to Phase B and C and then Phase A is the control wiring, then the equipment will work.
To determine this, you would typically require access to the equipment schematics to understand the precise connection of the control circuit.
 
I would never consider connecting any equipment to a high leg if the equipment has a neutral connection.

Even if the equipment doesn't require a neutral you need to make sure the equipment is ok being fed with a circuit having 208 volts to ground.
 
Electricalhelp said:
The equipment internally can be Connected to Phase A and B to run the equipment and then Phase C is the control wiring. If this is the case, then the equipment will not work.
But if the equipment internally can be Connected to Phase B and C and then Phase A is the control wiring, then the equipment will work.
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It would be connected to all three phases to run the equipment, and likely only to one phase to run the control wiring (most likely phase A). The aspects of this that concern whether it can be connected to a high leg system are:
1. Which phase(s) require nominal voltage-to-ground to not exceed 120V? Hook those up to the phase(s) that aren't the high leg.
2. Which phase(s) are used for control circuit wiring?
3. Is the equipment phase rotation sensitive? If you get it "wrong", swap the two standard phases to correct it. You can generally expect this for motor loads, and expect to ignore it for heating element loads.
 
Carultch said:
It would be connected to all three phases to run the equipment, and likely only to one phase to run the control wiring (most likely phase A). The aspects of this that concern whether it can be connected to a high leg system are:
1. Which phase(s) require nominal voltage-to-ground to not exceed 120V? Hook those up to the phase(s) that aren't the high leg.
2. Which phase(s) are used for control circuit wiring?
3. Is the equipment phase rotation sensitive? If you get it "wrong", swap the two standard phases to correct it. You can generally expect this for motor loads, and expect to ignore it for heating element loads.
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I was trying to find a way to explain to them what the issue is with the control wiring. Hence the example I shown to explain it to them.

But the questions you ask are important to ask the manufacturer to determine this information .

If Phase C is the High Leg for this case,
If I have a 240/1 Phase Equipment and I connect the equipment to Phase A and B only. I don't have to worry about the internal spec for the control wring since I avoided Phase C (High Leg).
 
Electricalhelp said:
I was trying to find a way to explain to them what the issue is with the control wiring. Hence the example I shown to explain it to them.

But the questions you ask are important to ask the manufacturer to determine this information .

If Phase C is the High Leg for this case,
If I have a 240/1 Phase Equipment and I connect the equipment to Phase A and B only. I don't have to worry about the internal spec for the control wring since I avoided Phase C (High Leg).
Click to expand...
Correct. If it is just single phase 120/240V equipment, it can connect to only the two standard phases, and the high leg is out of the picture. Both of the two standard phases are 120V to the grounded neutral, and it wouldn't matter which one of them powers the control circuits.
 
If the equipment specs calls for a 240V 4 or 5 wire circuit it likely uses a neutral for the control voltage, where the high leg placement could cause an issue.

If the specs call for a 3 wire Circuit 240/120 V its single phase, then don't pull a high leg to its outlet location. Use orange wire or tape on all high leg conductor's, as the NEC requires to prevent confusion by you or others that follow you.

If any of the equipment has a control transformer contained within to supply the control power, the high leg would not be an issue where it goes.
 
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