SE for 400 A

[Piramyd]

Hi there !
I relation with a residential SE 240/120 1ph - 400 A.
I would like to understand why an engineer would design the underground wires from the meter pedestal all the way 65 feet to the main panel
as (2) 2" C - 3#350 KCM + #3 Gnd .

Can I use use USE 400 KCM + 1#3 Gnd instead?
Thank you

 

[infinity]

The drawing shows parallel 350 kcmil, three of those is probably not going to fit in any 2" raceway. Also there should not be a #3 EGC in those raceways. An EGC is not required. As drawn the size of the #1/0 GEC to the water main is too small. You can use a single set of larger conductors if you want. With the 83% rule 400 kcmil copper would work.

 

[Piramyd]

Thank you very much.
I paid $400 for this design !!!
You said the GEC is not necessary.
Is this because you have the main panel hooked up to the UFFER
and the pedestal has a ground rod ?

 

[infinity]

I said that the EGC is not needed and would be in parallel with the neutral so it's not even permitted to be in the raceways. All of the metal components on the line side of the service disconnects are connected directly the the neutral there are no EGC's ahead of the service disconnects.

 

[Piramyd]

Just to learn because this is my first installation of this type with pedestal meter.

I would like to clarify the point of the #3 GND -----> ( (2) 2" C - 3#359 KCM + #3 Gnd . )

I believe that a meter pedestal is considered as a separate bldg and the pedestal should has its own ground road .

Aslo, it seems to me that the only point where the neutral at the pedestal is joining to EGC ( green wire) and GEC, is right on the pedestal .( it seems to be the bonding jumper)

So, if I do not run the #3 wire ( correct or incorrect gauge) from the main panel to the pedestal neutral/EGC joining point, from where, I should take EGC for the rest of the house?
Just from the UFFER hooked up to the main panel ground bar?
Trying to understand.
Thank you very much for your help.

 

[Dennis Alwon]

My assumption is that the pedestal just has a meter. If it is a meter and not a meter/main then no equipment grounding conductor is needed as Trevor stated. If it is a meter main -no reason to do that, it would need the equipment grounding conductor.

You would need 500 kcm copper and then the calculated load cannot be more than 380 amps. You could do that but you would have to increased the conduit size and get an okay from the architect

 

[Piramyd]

@dennis
Yes, the pedestal has a meter and service disconnect. !

 

[Dennis Alwon]

Then you do need the equipment grounding conductor

 

[infinity]

@dennis
Yes, the pedestal has a meter and service disconnect. !

The drawing does not show an OCPD in the pedestal but if there is one then the #3 EGC is too small for 400 amps with 350 kcmil conductors.

 

[Piramyd]

Thank both you guys

 

[augie47]

To me, none of it makes any sense. A single 350 isn't large enough as Infinity points out and if it was you can't get (3) in a single 2" conduit.
I see (2) 2" conduits. If we are talking Cu, you could parallel 2/0s and add a #3 equipment ground if necessary.

 

[winnie]

The engineer missed that when the circuit conductors are increased in size, the EGC also must be increase. #3 Cu is sufficient EGC for a 400A circuit if other rules don't come into play. See 250.122(B)

It looks like the #6 Cu EGCs after the 200A disconnects also need to be increased in size.

The drawing doesn't show a disconnect in the meter pedestal. The grounding system (GEC, EGC, bonded metal, etc) is connected to the neutral at the service disconnect, so the EGC only makes sense if there is a disconnect in the meter pedestal.

-Jon

 

[winnie]

To me, none of it makes any sense. A single 350 isn't large enough as Infinity points out and if it was you can't get (3) in a single 2" conduit.
I see (2) 2" conduits. If we are talking Cu, you could parallel 2/0s and add a #3 equipment ground if necessary.

I am guessing 2x350kcmil in parallel for each of the circuit conductors but you are quite correct; 3x350kcmil won't fit in each conduit as specified. Also surprising that the neutral would be full size.

-Jon

 

[suemarkp]

Is that all there is to the design, or are materials specified elsewhere. Seems awful for $400... TheThe 200A feeders seem to be mixing materials if the wire sizes are to be believed (4/0 Al for the grounded/ungrounded, #6 cu for the equipment ground). Could be the same for the paralleled feeders too. And the parallel 350's main power feeder seems grossly oversized. Don't know why he'd do that for a short run.

 

[infinity]

The design is all over the place, above the switchboard it says "SES, 400 amp service" so that would indicate no OCPD in the pedestal because the service is at the switchboard.

 

[Piramyd]

Ok Guys, thank you for all your time and interest to help me.
The 400 A main panel is already installed. The project was sopped for Owner economical reasons.
We are working again and we should install the meter/Disconnect pedestal.
As you see the UFFER is hooked up to the main panel.
This project is located at Henderson NV.
Last time the inspector stoped by there forced us to install isolated EGC from the main panel
to the pedestal . Now I'm looking for the adequate Pedestal and I'm figuring out if it should have
disconnect to be coherent with the inspector and what Jon said:

The drawing doesn't show a disconnect in the meter pedestal. The grounding system (GEC, EGC, bonded metal, etc) is connected to the neutral at the service disconnect, so the EGC only makes sense if there is a disconnect in the meter pedestal.

.