Weird situation

[hhsting]

I have 480V three phase coil line that has three phase motor. That’s the only load

The incoming service from panelboard is 208/120V three phase

So they placed a regular dry type distribution with primary voltage of 480V delta terminals H1,H2,H3 to secondary 240/120V wye terminals X1,X2,X3,X0 dry type transformer.

Only thing is the transformer is wired reversed so primary now is 208V and no neutral is brought to the X0 terminal. So I have three phase conductors and EGC brought.

The secondary now is 480V of course has no neutral terminal it’s H1, H2, H3 and has EGC but not the same size as the primary.

Questions:

1. Would the above be Separately derived system (SDS) or non separately derived system (NSDS)? Only load I have is three phase motor secondary.

2. How can one go about grounding if it is SDS no neutral is brought and which side 208V or 480V should be grounded?

3. Does the secondary 480V side require breaker protection and what about secondary cable size for the transformer?

4. Manufacturer datasheet says primary 480V delta and secondary 208/120V. By using it in reverse it’s not in compliance with NEC 2014 Section 110.3(B)? Any thoughts opinions

 

[__dan]

1. The 480 V delta secondary is separately derived, constructed as stated. You can add a system bonding jumper and GEC to one leg and reference that leg to ground, making it a corner grounded delta secondary.

2. see 1. You do not want any connection to the primary side neutral. X0 at the primary (properly) floats, constructed as stated. Primary side EGC is common or bonded to the secondary side EGC and to the system bonding jumper and GEC, all connected at the same (one) place.

3. IDK. I would have to check but it's possible primary side only OCPD may be allowed. Secondary side cable is sized to the load, so for the motor, ampacity is 125% of motor FLA.

4. Contact the manufacturer and inquire if reverse feeding is allowed. They may say something like 'allowed but not recommended' which would comply.

Likely the motor has tap connections for 480 / 240 - 208, so it's possible that you maybe don't need the distribution transformer and can run it at 208 V with tap changes at the motor, or at 240 V with a (much smaller) buck boost autotransformer.

 

[hhsting]

1. The 480 V delta secondary is separately derived, constructed as stated. You can add a system bonding jumper and GEC to one leg and reference that leg to ground, making it a corner grounded delta secondary.

2. see 1. You do not want any connection to the primary side neutral. X0 at the primary (properly) floats, constructed as stated. Primary side EGC is common or bonded to the secondary side EGC and to the system bonding jumper and GEC, all connected at the same (one) place.

3. IDK. I would have to check but it's possible primary side only OCPD may be allowed. Secondary side cable is sized to the load, so for the motor, ampacity is 125% of motor FLA.

4. Contact the manufacturer and inquire if reverse feeding is allowed. They may say something like 'allowed but not recommended' which would comply.

Likely the motor has tap connections for 480 / 240 - 208, so it's possible that you maybe don't need the distribution transformer and can run it at 208 V with tap changes at the motor, or at 240 V with a (much smaller) buck boost autotransformer.

I don’t follow. Is your numbers 1 and 2 method of grounding and bonding in NEC 2014 section 250.30 anywhere? When you say one leg you mean one of the phases? I thought system bonding jumper is like main bonding jumper connects grounded conductor to EGC?

 

[ptonsparky]

Nm

 

[ptonsparky]

You don’t have a grounded conductor on the secondary of a transformer until YOU make it.
Typically it would be the center point for a Wye.
Delta would be one of the secondary phases, if you want it grounded. Look at the transformer label or installation manual. Depends on what you have and what you want to do.

 

[__dan]

I don’t follow. Is your numbers 1 and 2 method of grounding and bonding in NEC 2014 section 250.30 anywhere? When you say one leg you mean one of the phases? I thought system bonding jumper is like main bonding jumper connects grounded conductor to EGC?

From memory it's 250.30 A 3 or (A 4 for multiple SDS on a shared GEC). But that only tells you what is required if you make it a grounded system.

Last time I checked, a floating delta secondary is still allowed with signage and ground fault monitoring, but I would usually never advise that. Most people familiar with the work expect the breaker to trip for faults to ground, which the floating delta will not do.

It's a different code reference if the SDS delta secondary is a system required to be grounded. If you choose to ground the delta secondary, then 250.30 A 3 applies. A 1 applies for the system bonding jumper (to any one phase leg of the delta). Do not connect anything to X0 at the primary.

 

[winnie]

I have 480V three phase coil line that has three phase motor. That’s the only load

The incoming service from panelboard is 208/120V three phase

So they placed a regular dry type distribution with primary voltage of 480V delta terminals H1,H2,H3 to secondary 240/120V wye terminals X1,X2,X3,X0 dry type transformer.

If this thread is connected to your other thread about the T3030K0023B transformer, then you also have the problem that you have a 208V supply going to a 240V transformer coil. The HV output will be nominal 437V.

Questions:

1. Would the above be Separately derived system (SDS) or non separately derived system (NSDS)? Only load I have is three phase motor secondary.

It is an SDS

2. How can one go about grounding if it is SDS no neutral is brought and which side 208V or 480V should be grounded?

A 'separately derived system' is something like a transformer secondary coil or a generator which produces electrical power without a direct conductive connection to the originating system. The transformer as a whole is not the SDS, rather the 'galvanically isolated' (no conductive current path) transformer secondary is the SDS. So grounding is _always_ on the secondary side as used. I your case the 480V side would need to be grounded.

An SDS gets grounded by intentionally connecting one of its terminals to ground. Generally you connect the 'closest to neutral' terminal to ground, eg the actual neutral of a wye, the 'midpoint' of a delta with a center tap, or a 'phase' terminal of a delta.

If you are running a VFD fed motor, you really really really want a WYE with a neutral ground connection.

3. Does the secondary 480V side require breaker protection and what about secondary cable size for the transformer?

In general, yes, the secondary of a transformer requires its own breaker protection. In the case of a delta:delta transformer, _primary_ OCPD may serve as the secondary protection if the primary OCPD is sized to protect the secondary conductors.

4. Manufacturer datasheet says primary 480V delta and secondary 208/120V. By using it in reverse it’s not in compliance with NEC 2014 Section 110.3(B)? Any thoughts opinions

If the manufacturer identifies primary and secondary, then the transformer is not in compliance. If the manufacturer identifies 'high voltage' and 'low voltage', then it is. Some transformers are identified for reverse feed operation, some are not.

-Jon

 

[hhsting]

Do I use 250.30(A) or 250.30(B)? I looked at 250.30(A)(1)(3) says grounded conductor. I have no grounded conductor(neutral) 480V delta secondary side so how can their be system bonding jumper?

 

[kwired]

Do I use 250.30(A) or 250.30(B)? I looked at 250.30(A)(1)(3) says grounded conductor. I have no grounded conductor(neutral) 480V delta secondary side so how can their be system bonding jumper?

This:

You don’t have a grounded conductor on the secondary of a transformer until YOU make it.
Typically it would be the center point for a Wye.
Delta would be one of the secondary phases, if you want it grounded. Look at the transformer label or installation manual. Depends on what you have and what you want to do.

Your secondary in this case only has the three "phase conductors" there is no neutral to ground so you have to ground one of those phase conductors, which makes it a "corner ground" system.

 

[hhsting]

Alright and 480V delta secondary conductors size and EGC based on 208V primary breaker? No supply side bonding jumper and secondary breaker 480V delta side? No 240.21(C), 250.30(A)(2)?

 

[kwired]

Alright and 480V delta secondary conductors size and EGC based on 208V primary breaker? No supply side bonding jumper and secondary breaker 480V delta side? No 240.21(C), 250.30(A)(2)?

Secondary of SDS will need a main bonding jumper, that is what makes it a grounded system. Whether or not you must have a secondary OCPD depends on conditions. Three wire delta to three wire delta is a situation where you can protect the secondary with the primary OCPD, still need to ground something on the secondary unless using ground fault detection system. You have wye to delta setup, pretty much need to have secondary OCPD.

 

[ptonsparky]

The secondary protection can be what you use to protect your motor.

I would be using a Pump Panel for this situation. They are suitable for use as service disconnects. At least the ones I use are.