MBJ in industrial control panel, redesign G&B

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housemoney

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Existing NRTL listed control panel in the field being retrofitted with a non separately derived system standby generator... interested in feedback to clean this G&B up:

I've perused through article 250 and UL 508a but seem to be going in circles:


  1. Relocate the Service MBJ from Control Panel backplate to inside of service disco.
  2. Only existing Grounding Electrode is well casing currently -green EGC to well pump is pigtailed under well cap.
    1. re-route this EGC/GEC to Disco Ground bus or:
    2. separate the well pump EGC and GEC to well casing?
  3. Bond EGC Bus in Disco to Existing EGC bus or new L125 lug on lower area in control panel?
  4. Drive supplemental ground rod? Bond bare #6 to EGC bus in Disco?
  5. Bond 24V side of Control XFMR in Control panel to EGC bus in control panel?


CP.jpg
 
I don't see how anything would need to change if the new generator is not a SDS.

Control transformers 1000VA and under do not require connection to a GEC. This is found in both the NEC and UL508a.
 
petersonra said:
I don't see how anything would need to change if the new generator is not a SDS.

Control transformers 1000VA and under do not require connection to a GEC. This is found in both the NEC and UL508a.
Click to expand...
It's hard to tell in that picture but that Transformer looks much bigger than 1000 VA

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just got the as built, control XFMR is rated 1KVA

At the very least I want to get the MBJ relocated into the disco enclosure?
 
housemoney said:
just got the as built, control XFMR is rated 1KVA

Not surprising since UL discourages control transformers > 1000 VA.

At the very least I want to get the MBJ relocated into the disco enclosure?
Click to expand...

Why do you want to move the MBJ?

If the panel is listed as service entrance equipment the MBJ can be located there. However, UL508a requires that a disconnecting means be part of a UL508a panel that is service equipment and I don't see a disconnecting means in the cabinet.
 
I typically to keep the MBJ/bonding point in the service disconnecting means on generator setups not separately derived (no switched grounded conductor) . Preference probably happened due to a local AHJ in my early years... The disco is outside and to the right of the CP.

Thinking fault current impedance path back through that EGC bus on the lower part of the panel is bonded to the ground terminal block with a #14 stranded conductor is much less that across the backplate. Might just size that up a bit and call it good.
 
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