Unbonded secondary in transformer ??

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sundowner

sundowner

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West Wisconsin
Having a few issues recently in a commercial kitchen. ( intermittant voltage readings from ground to nuetral) Long story short...I discovered a transformer which feeds the kitchen panel board isn't bonded. I can get in the transformer and visually follow the secondary conductors, along with the primary conductors. The Nuetral buss (off the secondary) goes to the panel board with several 600 MCM's. No where is this installation bonded to tranformer case. I mentioned this to the engineer who actually ran the job, and he says in some cases (possibly a state spec??) this could be acceptable. My question is what gives?? I thought any time your dealing with a SDS, your creating a nuetral and it must be bonded to case, right ??

Any thoughts on this install, Is there something new that I'm totally missing??

Thanks guys
 
Assuming that this is a WYE transformer the system must be grounded. This can be either at the transformer or at the OCPD/disconnecting means on the secondary. Take a look at 250.20(B).
 
Thanks Infinity

Yes this is a 480/120Y, Delta to Wye trasformer, 225KVA. It is grounded but my nuetral point isn't properly bonded.( A Properly sized bonding jumper from the nuetral point of the secondary to the transformer case) Just wondering if something has changed recently where this would be acceptable. If so, that could explain my sporadic voltages on the recorder from nuetral to ground up in the kitchen on some of the appliances. This started with several calls from a refridgerated open shelf cooler, where one of the contactor coils was burning up. I hung a recorder on the cooler and found some strange things. One being a voltage level between the nuetral and ground. Ultimately there was over 160 volts on my contactor coil. I suppose this was because nothing to pull my nuetral voltage down to earth potential is present.

So do I have a bonding issue here ?? I still think I do??
 
sundowner said:
One being a voltage level between the nuetral and ground. Ultimately there was over 160 volts on my contactor coil. I suppose this was because nothing to pull my nuetral voltage down to earth potential is present.

So do I have a bonding issue here ?? I still think I do??
Click to expand...

Yes you do. I encountered a similar situation a few years ago (where the bond that I instructed someone to install was not installed). On final check of voltages at the Panelboard of the SDS, I was reading different RMS values on each phase to ground, and was reading RMS voltage values from grounded (neutral) conductor to the grounding conductor. Created the system bond, and all values "leveled out."
 
do you mean a 480v primary and a 120/208v secondary? If this is the case your neuteral has to be bonded otherwise you wont get a constant 120 v it will be like a floating ground and you will have voltage readings all over the place..on all phases to neuteral . This type of system should be bonded to a cold water pipe and or ground rod and to the xmer case... 1/0 copper should do the trick...I dont know if this is acceptable where you are but bonding within 5 feet of the main water of a building can be a pain, so what we do is from the xmer run the 1/0 up to a steel beam that is continuous and welded together with the whole building structure attach it to the steel with a mechanical lug ( grinding off any paint so touches steel and use anti oxidation paste in between) and then go from building steel near the water main to the water main.. this will save alot of time and money and i uasually put both ends of the run in a 1 inch pvc just to be professonal.. and to protect it from physical damage...:)
 
Floating System

Floating System

Since I started this thread: http://forums.mikeholt.com/showthread.php?t=130382&highlight= ,I have found missing SBJ's and GEC's in churches, schools and other commercial buildings. It seems to be a recklessly common oversight.

It also very dangerous, because OCPD's may not trip on ground faults. Therefore, I disagree with your engineer. To me, the NEC is pretty clear on this matter.

The old thread is titled "floating neutral", a phrase which is commonly used to describe this condition, but is technically incorrect as Forum member Rick Christopherson capably describes.
 
copper chopper said:
do you mean a 480v primary and a 120/208v secondary? If this is the case your neuteral has to be bonded otherwise you wont get a constant 120 v it will be like a floating ground and you will have voltage readings all over the place..on all phases to neuteral .
Click to expand...

Voltage readings to neutral will all be consistant, voltage reading from phases as well as neutral to ground will float all over the place.


This type of system should be bonded to a cold water pipe and or ground rod and to the xmer case... 1/0 copper should do the trick...I dont know if this is acceptable where you are but bonding within 5 feet of the main water of a building can be a pain, so what we do is from the xmer run the 1/0 up to a steel beam that is continuous and welded together with the whole building structure attach it to the steel with a mechanical lug ( grinding off any paint so touches steel and use anti oxidation paste in between) and then go from building steel near the water main to the water main.. this will save alot of time and money and i uasually put both ends of the run in a 1 inch pvc just to be professonal.. and to protect it from physical damage...:)
Click to expand...

It is important to bond the grounding electrode system of the transformer secondary to the grounding electrode system of the primary. Water pipe or building steel accomplishes this. If you don't have water pipe or building steel you must still connect to the grounding electrode of the supply somehow.


sundowner
Thanks Infinity

Yes this is a 480/120Y, Delta to Wye trasformer, 225KVA. It is grounded but my nuetral point isn't properly bonded.( A Properly sized bonding jumper from the nuetral point of the secondary to the transformer case) Just wondering if something has changed recently where this would be acceptable. If so, that could explain my sporadic voltages on the recorder from nuetral to ground up in the kitchen on some of the appliances. This started with several calls from a refridgerated open shelf cooler, where one of the contactor coils was burning up. I hung a recorder on the cooler and found some strange things. One being a voltage level between the nuetral and ground. Ultimately there was over 160 volts on my contactor coil. I suppose this was because nothing to pull my nuetral voltage down to earth potential is present.

So do I have a bonding issue here ?? I still think I do??​
Click to expand...

It can have the bond at the transformer or at the first disconnect, if conductive material (including metal raceways)connects the two it can not be both, otherwise the neutral current has other paths between the disconnect and the transformer. If there is no bond at either your secondary is not grounded and is floating. Any unintentional grounds on the secondary will stabilize voltage but how solid the unintended connection is can make this unreliable. Keep in mind it can be a phase conductor that becomes grounded and you will not trip any overcurrent devices as long as no other conductor becomes grounded.

If all connections are good but there is no bonding jumper your system voltages will remain normal, just your references from each conductor (including the neutral) to ground will be floating all over the place
 
sundowner said:
Having a few issues recently in a commercial kitchen. ( intermittant voltage readings from ground to nuetral) Long story short...I discovered a transformer which feeds the kitchen panel board isn't bonded. I can get in the transformer and visually follow the secondary conductors, along with the primary conductors. The Nuetral buss (off the secondary) goes to the panel board with several 600 MCM's. No where is this installation bonded to tranformer case. I mentioned this to the engineer who actually ran the job, and he says in some cases (possibly a state spec??) this could be acceptable. My question is what gives?? I thought any time your dealing with a SDS, your creating a nuetral and it must be bonded to case, right ??

Any thoughts on this install, Is there something new that I'm totally missing??

Thanks guys
Click to expand...

The 'bonding' of the common point of a wye secondary to the transformer case itself is only meaningful if the case itself is connected to a grounding electrode or other means of grounding. I prefer the neutral/ground bond to be in the panel as its integrity is easier to observe.
 
A transformer (as a SDS) must be grounded if it has one of the secondary voltages/phases listed in 250.20 and yours meets that requirements
Transformers must have a grounding electrode system terminated at the same location the system bonding jumper is located, this can be at the transformer or at the first disconnecting means.
 
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