Is this required

[Alwayslearningelec]

Is the grounding in this detail required for adding a new switch as shown(tapping existing service)?

 

[infinity]

Since the largest GEC ever required is #3/0 the answer is no. The conductor sizes of that ground detail are not required.

 

[d0nut]

Those conductor sizes may not be required by the NEC, but if they are in the contract documents then they are required for the project.

 

[xformer]

IMHO... It might be required by job spec by the customer, or by AHJ, but not required by code.

 

[jaggedben]

Leaving aside the GEC size, and only speaking of code ..

It's required in part, and in part it depends.

The neutral to ground bond (Main Bonding Jumper) is required in all situations.

If the existing GEC installation lands the GEC(s) in the other service disconnect(s), then you must also bring a GEC tap to the new disconnect, as shown or similar to the drawing. The manner shown could be fine if the main building ground bus meets requirements. It is not the only place you could terminate the new GEC (or GEC tap) on the ground end.

If the existing GEC is connected further towards the utility, for example in the 'existing service end box', then the disconnect doesn't need its own GEC or GEC tap.

 

[infinity]

IMHO... It might be required by job spec by the customer, or by AHJ, but not required by code.

I think that was the OP's question, is it required by the NEC. Note 1 has many things that are not required, same with Note 4. Since conduit protection is not required add Note 3 to the list too.

 

[David Castor]

If it's shown in the Contract Documents, then it is required for this project as long as it isn't a code violation. The NEC is not a design guide.

 

[texie]

I see a number of issues with drawing the OP posted. For starters, there should not be a EGC on the supply side. Maybe a SSBJ depending on how this done but not a #1 EGC.

 

[petersonra]

Two 350 cu seems kind of excessive too.

I think this drawing was done by someone who does not know what they are doing and just made everything overkill to cover that lack of knowledge.

 

[Fred B]

Two 350 cu seems kind of excessive too.

I think this drawing was done by someone who does not know what they are doing and just made everything overkill to cover that lack of knowledge.

Maybe, but there is no indication on line drawing as to the length of the run that might need to increase size for voltage drop. Depending on the min size that might be installed then the EGC would be increased proportionally to the increase in the current carrying conductors, so the #1 EGC might be undersized.

 

[infinity]

Maybe, but there is no indication on line drawing as to the length of the run that might need to increase size for voltage drop. Depending on the min size that might be installed then the EGC would be increased proportionally to the increase in the current carrying conductors, so the #1 EGC might be undersized.

Since there is a 400 amp OCPD and over 600 amps worth of conductors I would say that the ungrounded conductors have been increased in size therefore the #1 may be too small. Given the other errors with this drawing I'm not surprised the designer got that wrong too.

 

[david luchini]

so the #1 EGC might be undersized.

The #1 egc appears to be adequately sized for increase in circular mils

 

[infinity]

The #1 egc appears to be adequately sized for increase in circular mils

I just eyeballed it like Fred, did you do the calculation?

 

[david luchini]

I just eyeballed it like Fred, did you do the calculation?

Yeah. #1 is 60% larger than #3. 700mcm is only 40% larger than 500mcm.

 

[electrofelon]

it would probably be good to clarify which side of the CT's the tap is made.

 

[Fred B]

Yeah. #1 is 60% larger than #3. 700mcm is only 40% larger than 500mcm.

Thanks for doing the math. Just eyeball like @infinity said. Was throwing out the possibility of oversize for voltage drop and then need to follow up with the EGC increase proportionally. Something most miss.

Something I see often is someone using 250kcmil for whatever reason when 4/0 would suffice but never increase the EGC proportionally from the #4.

Question would be if the math made for conductor proportion that is slightly larger than the 2 sizes up do you increase to 3 sizes or just use the 2 size increase, or use the over .5 rounding rule?

 

[infinity]

Just eyeball like @infinity said.

For my original eyeball I thought that since this installation uses parallel conductors if you used the minimum required size of parallel #3/0's (400 amps) the #1 is too small when applying 250.122(B). The minimum size would be #4/0. I'm rusty at these calculations so check my math.

#3/0=167800 cm
3/0*2=335600 cm
350,000*2=700000 cm

700 kcmil/335.6 kcmil = 2.09 ratio of size increase
#3=52620 cm
52620*2.09= 109.7 kcmil
#1/0= 105.6 kcmil too small
#2/0= 133.1 kcmil correct size.

Edit: I corrected the error, thanks Tulsa!

 

[Tulsa Electrician]

For my original eyeball I thought that since this installation uses parallel conductors if you used the minimum required size of parallel #3/0's (400 amps) the #1 is too small when applying 250.122(B). The minimum size would be #4/0. I'm rusty at these calculations so check my math.

#3/0=167800 cm
3/0*2=335600 cm
350,000*2=700000 cm

700 kcmil/335.6 kcmil = 2.09 ratio of size increase
#1=83690 cm
83690*2.09= 175 kcmil
#3/0= 167.8 kcmil too small
#4/0= 174912 correct size.

You based it off of the #1 cu.
Wouldn't you base it off the minimum EGC required for the 400 amp. Which would be #3 cu @ 2.08581 ?
52620* 2.08581= 109,755.3222
2/0@ 133,100 CM

 

[infinity]

You based it off of the #1 cu.
Wouldn't you base it off the minimum EGC required for the 400 amp. Which would be #3 cu @ 2.08581 ?
52620* 2.08581= 109,755.3222
2/0@ 133,100 CM

Yes you would. As I said a little rusty but my initial guess that the #1 could be too small was accurate. I made the correction to my last post.

 

[Fred B]

Are you sizing the EGC from the potential full size wire for amperage or the parallel conductor size?