TRANSFORMER SECONDARY CONDUCTORS

[GoldDigger]

It also helps a lot if when quoting in a reply and then editing the reply we do not accidentally edit out part or all of the automatically included QUOTE tags.
If the time for the individual poster to edit has passed, only a Moderator will be able to jump in and make it more readable. (looking specifically at post # 9 in this thread. )

 

[ohmhead]

You need both a neutral and a supply side bonding jumper between the transformer and the first OCPD.

OK lets take a 75 KVA 480 /208-120 V 3PH transformer secondary is lets say phase conductors are 300KCML ALU with a 1/0 ALU supply side bonding jumper In each case we bond the neutral to metal ground inside the transformer the neutral or grounded conductor even if it is uncut a single conductor looping back down directly to metal case of transformer is not to code ?
The 1/0 is the supply side bonding jumper and we run that with the secondary phase & grounded conductor to the load or panel .

Please explain why if i use the grounded conductor and connect to the neutral bus with a lug in the transformer then without a splice pass it directly with a loop to the metal case were all grounds are connected inside the grounding electrode conductor building steel cold water . That it still needs supply side bonding jumper attached to metal case and to neutral bus inside transformer . Which in most cases is smaller than the grounded conductor ?

 

[infinity]

OK lets take a 75 KVA 480 /208-120 V 3PH transformer secondary is lets say phase conductors are 300KCML ALU with a 1/0 ALU supply side bonding jumper In each case we bond the neutral to metal ground inside the transformer the neutral or grounded conductor even if it is uncut a single conductor looping back down directly to metal case of transformer is not to code ?
The 1/0 is the supply side bonding jumper and we run that with the secondary phase & grounded conductor to the load or panel .

Please explain why if i use the grounded conductor and connect to the neutral bus with a lug in the transformer then without a splice pass it directly with a loop to the metal case were all grounds are connected inside the grounding electrode conductor building steel cold water . That it still needs supply side bonding jumper attached to metal case and to neutral bus inside transformer . Which in most cases is smaller than the grounded conductor ?

So you're asking if you could use the secondary neutral conductor also as the system bonding jumper by connecting it to the transformer case on it's way to the OCPD in the remote enclosure?

We typically do that with the GEC when it's the same size as the required SBJ with a lay in style lug..

 

[ohmhead]

So you're asking if you could use the secondary neutral conductor also as the system bonding jumper by connecting it to the transformer case on it's way to the OCPD in the remote enclosure?

We typically do that with the GEC when it's the same size as the required SBJ with a lay in style lug..

Yes that's what iam asking do you see a problem with that per the NEC

 

[don_resqcapt19]

OK lets take a 75 KVA 480 /208-120 V 3PH transformer secondary is lets say phase conductors are 300KCML ALU with a 1/0 ALU supply side bonding jumper In each case we bond the neutral to metal ground inside the transformer the neutral or grounded conductor even if it is uncut a single conductor looping back down directly to metal case of transformer is not to code ?

That would be the system bonding jumper and not a supply side bonding jumper.

The 1/0 is the supply side bonding jumper and we run that with the secondary phase & grounded conductor to the load or panel .

From your previous post it was not clear that you were installing a supply side bonding jumper along with the phase conductors and the grounded conductor between the transformer and the first overcurrent protective device.

Please explain why if i use the grounded conductor and connect to the neutral bus with a lug in the transformer then without a splice pass it directly with a loop to the metal case were all grounds are connected inside the grounding electrode conductor building steel cold water . That it still needs supply side bonding jumper attached to metal case and to neutral bus inside transformer . Which in most cases is smaller than the grounded conductor ?

The issue is the code terminology. You need both a system bonding jumper and a supply side bonding jumper. They are not the same thing. The looped grounded conductor is acting as the system bonding jumper and not as a supply side bonding jumper.

 

[hurk27]

OK lets take a 75 KVA 480 /208-120 V 3PH transformer secondary is lets say phase conductors are 300KCML ALU with a 1/0 ALU supply side bonding jumper In each case we bond the neutral to metal ground inside the transformer the neutral or grounded conductor even if it is uncut a single conductor looping back down directly to metal case of transformer is not to code ?
The 1/0 is the supply side bonding jumper and we run that with the secondary phase & grounded conductor to the load or panel .

Please explain why if i use the grounded conductor and connect to the neutral bus with a lug in the transformer then without a splice pass it directly with a loop to the metal case were all grounds are connected inside the grounding electrode conductor building steel cold water . That it still needs supply side bonding jumper attached to metal case and to neutral bus inside transformer . Which in most cases is smaller than the grounded conductor ?

I think if you think of the supply side bonding jumper like an EGC, but sized as a GEC you might understand it better, because it is at or ahead of the disconnect on the secondaries of the transformer but does not create another parallel path between the grounded conductor and the panel case, it is basically an EGC sized to table 250.66, also the SSBJ can be a non-flexible metal raceway between the transformer and the panel as long as bonding bushings are installed.

Here is a equivalent service example of the SSBJ lets say you have a meter base with an isolated neutral terminal block that isolates the neutral from the meter case, also you have PVC between the meter and the main breaker panel, if you bonded the neutral in the panel you would then have to run a bonding jumper back to the meter and bond the case, this conductor would also have to be sized per table 250.66, but then you could also just bond the neutral at the meter and the panel so that is why we don't see it much.

So if you understand that if a metal raceway is installed between the transformer and first disconnect you can bond the neutral at the panel or at the disconnect but not both, then you must install a SSBJ from the point you bonded the neutral to the others case, if you have run PVC then you are allowed to bond the PVC at both the transformer and at the first disconnect or run a SSBJ between them.

The system bonding jumper is the same as the main bonding jumper for a service, if you have a main breaker panel fed from a transformer you can even use the screw it comes with as the system bonding jumper just like you do for a service, or you have to use a wire, but just like a service the GEC's must land with the neutral on the same bus bar because the screw would not be allowed in between 250.24.

If you have a install that is small enough that table 250.66 is not sizing the conductor over 3/0 then using the system bonding jumper to also feed out to the grounding electrode is fine, but if it is a larger install where the 12.5% comes into play it would not make sense to do this as the GEC stops at 3/0 but the system bonding jumper will be required to meet the 12.5%

 

[GoldDigger]

... if you have run PVC then you are allowed to bond the PVC at both the transformer and at the first disconnect or run a SSBJ between them.

???

 

[infinity]

I think if you think of the supply side bonding jumper like an EGC, but sized as a GEC you might understand it better, because it is at or ahead of the disconnect on the secondaries of the transformer but does not create another parallel path between the grounded conductor and the panel case, it is basically an EGC sized to table 250.66, also the SSBJ can be a non-flexible metal raceway between the transformer and the panel as long as bonding bushings are installed.

Where can one find the requirement for bonding bushings when using a non-flexible raceway?

 

[ohmhead]

That would be the system bonding jumper and not a supply side bonding jumper.

From your previous post it was not clear that you were installing a supply side bonding jumper along with the phase conductors and the grounded conductor between the transformer and the first overcurrent protective device.


The issue is the code terminology. You need both a system bonding jumper and a supply side bonding jumper. They are not the same thing. The looped grounded conductor is acting as the system bonding jumper and not as a supply side bonding jumper.

Yes I agree we do need both and we have both Iam just trying to understand the code and the words jumper which is confusing the issue a least for me .

Ok so the system bonding jumper is the jumper that goes from neutral to metal case of the transformer. yes /no the supply side bonding jumper is from secondary of transformer in the raceway that is running to the first overcurrent protective device . yes /no

Now we do install both on all our transformers I just don't use the technical terms I guess correctly . Whats confusing is the term bonding jumper and not grounding conductor but I do understand its a system bonding jumper which is the grounding conductor with the phase conductors . To me a jumper is a short wire between two points not a grounding conductor running 25 feet .

Iam just asking to get this clear in my head can you say yes or no then I can tell which is which .

 

[hurk27]

???

250.30(A)(1) Exception 2

Exception No. 2: A system bonding jumper at both the
source and the first disconnecting means shall be permitted
if doing so does not establish a parallel path for the
grounded conductor. If a grounded conductor is used in this
manner, it shall not be smaller than the size specified for the
system bonding jumper but shall not be required to be larger
than the ungrounded conductor(s). For the purposes of this
exception, connection through the earth shall not be considered
as providing a parallel path.

 

[hurk27]

Where can one find the requirement for bonding bushings when using a non-flexible raceway?

Ya me had a brain fart, for some reason had services in mind and 250.92 I think it was of being ahead of a main disconnect as 250.92 is for services.

 

[hurk27]

Yes I agree we do need both and we have both Iam just trying to understand the code and the words jumper which is confusing the issue a least for me.

Ok so the system bonding jumper is the jumper that goes from neutral to metal case of the transformer. yes /no

Yes or if you install it at the first disconnect, it can be the screw or strap that we use to bond the neutral bar to the case of the disconnect when used as a service disconnect.

the supply side bonding jumper is from secondary of transformer in the raceway that is running to the first overcurrent protective device . yes /no

kind of, it is the bonding conductor you run from the neutral bar in the transformer to the grounding bar or case in the first disconnect.

Remember if you install the system bonding jumper in the transformer then you run it from the transformer neutral bar to the grounding bar or case in the disconnect the neutral is kept separate in the disconnect, if the system jumper is made at the first disconnect then you run it from the neutral bar or case in the first disconnect to the case grounding bar in the transformer and the neutral is kept isolated in the transformer, the GEC is run to the neutral bar where ever the system bonding jumper is installed be it in the transformer or first disconnect.

Now we do install both on all our transformers I just don't use the technical terms I guess correctly . Whats confusing is the term bonding jumper and not grounding conductor but I do understand its a system bonding jumper which is the grounding conductor with the phase conductors . To me a jumper is a short wire between two points not a grounding conductor running 25 feet .

Iam just asking to get this clear in my head can you say yes or no then I can tell which is which .

 

[GoldDigger]

250.30(A)(1) Exception 2

I would call that bonding the panel at each end of the PVC, not bonding the PVC itself.

Tapatalk!

 

[hurk27]

I would call that bonding the panel at each end of the PVC, not bonding the PVC itself.

Tapatalk!

A'hhh I didn't catch the typo, yep that was what I meant, just didn't get the brain to connect with my fingers to type it.:ashamed:

I have no idea why I typed PVC instead of the word neutral?

 

[ohmhead]

250.30(A)(1) Exception 2

I don't bond at both disconnect and transformer I only jumper the neutral at the transformer .
So we would not need the exception in my case .

This post was informative basically the only thing I needed was to define the two SSBJ / SBJ and use the correct NEC table & rules. Which is the grounding conductor and to distinguish the bonding jumper from the grounding conductor that runs with the phase and neutral in raceways. .

The ability to use the NEC as written for this part was unclear to the average electrician working in the trade that has been out of school for many years .
We install our work with engineered plans our inspector questioned this and he was correct in addition I learned that what is on the plans maybe incorrect .
In that we must be able to read the NEC which to me is not clear theres to many parts to no pun intended that jumper around back and forth .

I don't want to dolt on this but after reading this I never did get a comfort zone on the wire sizes which relate to the each electrically .

If you had a fault on the system in the raceways and the lets say 3/0 lesser wire size was used by code in some cases to me the branch grounding table would be better for both SB jumpers . A larger conductive ground would handle the surge of current . YES/NO Would the breaker trip faster or slower and iam thinking primary in this case I know there is no protection between secondary and first disc ? And in which case would this be a issue not that it happens everyday but if you had a major issue whats your thoughts reasoning or ramifications.

My thought is current during a fault across phases and grounds a crow bar effect or a cross to ground would be better controlled by a larger bond size . That a smaller bond would give a high resistance in circuit and increase the time of trip .

 

[don_resqcapt19]

The supply side bond jumper and the system bonding jumper (if of the wire type) will almost always (EGCs installed in raceways for a parallel systems may be larger) be larger than an EGC sized from Table 250.122. There is no 3/0 maximum for supply side bonding jumpers or system bonding jumpers. If the phase conductors are over 1100 kcmil, then these two jumpers are sized at 12.5% of the phase conductors. The confusion on this issue was one of the reasons that, in the 2014 code, we have a new Table 250.102 that is used for sizing supply side and system bonding jumpers among other things.

 

[infinity]

The supply side bond jumper and the system bonding jumper (if of the wire type) will almost always (EGCs installed in raceways for a parallel systems may be larger) be larger than an EGC sized from Table 250.122. There is no 3/0 maximum for supply side bonding jumpers or system bonding jumpers. If the phase conductors are over 1100 kcmil, then these two jumpers are sized at 12.5% of the phase conductors. The confusion on this issue was one of the reasons that, in the 2014 code, we have a new Table 250.102 that is used for sizing supply side and system bonding jumpers among other things.

Has the inclusion of the new table changed anything or was it just added for ease of use?

 

[texie]

Has the inclusion of the new table changed anything or was it just added for ease of use?

No, the end result is the same. As I mentioned in my earlier post, I think this was done to help make this more clear. Lot's of people struggle with this as we can see. And as you and others have mentioned, half the battle in learning these things is using and understanding the right terms. It goes a long way in understanding.

 

[ohmhead]

The supply side bond jumper and the system bonding jumper (if of the wire type) will almost always (EGCs installed in raceways for a parallel systems may be larger) be larger than an EGC sized from Table 250.122. There is no 3/0 maximum for supply side bonding jumpers or system bonding jumpers. If the phase conductors are over 1100 kcmil, then these two jumpers are sized at 12.5% of the phase conductors. The confusion on this issue was one of the reasons that, in the 2014 code, we have a new Table 250.102 that is used for sizing supply side and system bonding jumpers among other things.

Ok now were really confused help me out here Don .

In post 13# Infinity shows by example 6 runs of 600 =3600 x 12.5% = 450 mcm ALU / SBJ which is the short jumper from ground case to neutral .

Then he shows 600 mcm phase in each raceway Table 250.66 = 3/0 ALU/ SSBJ in each paralleled raceway as joe mentioned in the previous post .

So was this a correct statement in this post because our one line schedule shows 6 runs of 600 mcm and the SSBJ is a 500 mcm one in each raceway .
to me the engineer is using the 12.5 % for the SSBJ . How did he come up with 500mcm iam thinking he used 12.5 % ?

 

[infinity]

Ok now were really confused help me out here Don .

In post 13# Infinity shows by example 6 runs of 600 =3600 x 12.5% = 450 mcm ALU / SBJ which is the short jumper from ground case to neutral .

Then he shows 600 mcm phase in each raceway Table 250.66 = 3/0 ALU/ SSBJ in each paralleled raceway as joe mentioned in the previous post .

So was this a correct statement in this post because our one line schedule shows 6 runs of 600 mcm and the SSBJ is a 500 mcm one in each raceway .
to me the engineer is using the 12.5 % for the SSBJ . How did he come up with 500mcm iam thinking he used 12.5 % ?

He could be using the 12.5% rule for the SSBJ in each raceway but it's not required. If you had only one raceway, say a wireway, then you would have only one SSBJ which would need to be sized according to the 12.5%.