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Joined: Jul 2002
Posts: 6
CAB Offline OP
Junior Member
Suppose I have an existing 120/240v 200amp single phase panel which the client wants to retain as a sub-panel on a new upgraded 120/208v 600amp 3p 4w service. This is a small service station being converted to a auto car wash. What changes, if any, must be made to the single-phase panel in order to make the switch. Also, must the 600amp panel be sized to include the 200amp single phase sub-panel load. Can the panels be run side-by-side with the sub-panel tapped in above the main panel so that only the CT and service & entrance conductors are sized for the total load?

Thanx in advance [Linked Image])


Joined: Oct 2000
Posts: 5,392
I would ask if the 600a panel is rated for a 200a breaker, sub out the old 200a panel, redirect major loads to the 600a

[This message has been edited by sparky (edited 08-05-2002).]

Joined: Apr 2001
Posts: 507
separate the grounds and neutrals for the sub-panel.

I think that the tap you are suggesting is legal.....but definitely not preferred in my book. Much better to do what sparky said and run the sub off a breaker in the main panel.


Joined: Aug 2002
Posts: 4
Junior Member
is this a laserwash by any chance?
i'm doing one right now, but from the ground up. its a 3 bay auto with 3 wand bays as well.
the loads should be taken into consideration when sizing the service.
the existing panel should be converted to a subpanel as per code specs and could be fed from a lug kit ordered with the panelboard to save the cost of a 200 amp breaker.
the units being installed on my job require a 200 amp, 3-phase/208 volt breaker each, plus the additional lighting and motor loads.
and yes you can install them side by side.

Joined: Apr 2002
Posts: 2,527
It may be worth verifying beforehand that existing 240V load(s) will not have problems at 208V.

Joined: Jul 2002
Posts: 6
CAB Offline OP
Junior Member
According to the utility company, the afc is 15,613 amps for the new 120/208 3p 4w service, however the interrupt rating for the old 200amp 120/240 1p panel is 10,000 amps sym at 240v. Can I protect this old panel with a 200 amp fuse rated to the new afc?

btw danger: this is a Vector Washing system, probably very similar to the Laserwash.

Joined: Oct 2000
Posts: 2,723
Likes: 1
Broom Pusher and
This sounds like a project which should have been designed by an EE [just my $0.02], but since you are willing to overtake this task, let's see if we [all in this Forum] can assist enough here.

Leaving the existing 200 amp 1 phase 3 wire panel and making it a subpanel is a good idea - provided this will be adequate for the loads [I'll expand on this].
I guess this was originally the Main Service panel??? If so, do as was suggested and be sure the Grounded Conductor's bus is Isolated from the enclosure [AKA not grounded in this panel]. Be sure to remove any EGCs from the bus and place them on a grounding bus strip [may be easier to place the Grounded Conductors on a new Isolated Bus and leave the existing bus with the EGCs as is].

As to leaving the bus kit as 1 phase 3 wire, this [as far as I know] is NEC compliant. It just brings up imbalance issues [and is strange to us "Veteran 3 phase guys"... humor].
If the loads which shall be connected to this panel would require 3 phase, or if there would be an advantage to having 3 phase 4 wire circuitry, then change the bus kit to a 3 phase 4 wire one and add the 3rd Ungrounded Conductor to the panel.
This will all be determined by what the connected loads need.

Per the SCA quoted by the PoCo [Utility Engineers], this would be the minimum 3 phase "Bolted" available fault current level at the Service.
If the subpanel in question is far enough away to reduce the SCA level far below 10KAIC, then you may use the 10KAIC breakers in the subpanel. If the SCA is 10KAIC or above at the subpanel, the existing 10KAIC frames would need to be changed out for 22KAIC ones [unless you try for a Series Rated Type System, which will be really difficult to accomplished and may become extremely expensive if the existing panel is older equipment].

The Subfeeder OCPD would need to be rated above the SCA quoted level found at the main service [not less than 22KAIC]. This could be accomplished by using RK5 type fuses in the switch in the gear section. RK5s are rated 200KAIC.
If a MCCB is used in the switchgear section, it would need a rating of not less than 22KAIC.

Let us know if these items help and if you have further questions.

Scott S.E.T.

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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