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Thank you @FacEngrPE, good idea. Murphy loves administrative controls.

This is a critical load so customer has two UPS's. However, they will never be paralleled as OEM says "don't". They wanted the redundancy for UPS maintenance and/or failure and for the extended battery period if needed for long outages. I found that the UPS Q3 breaker is 4 pole. They may need to...

After closing CBA2-3, the neutral path back to XFMR-2 could travel through XFMR-3's neutral wire then through the ground path to XFMR-2 depending on the path of least resistance. Is this a common occurrence with tie switches on 4 wire systems?

Got it! Thank you! I couldn't get my mind around the fact the neutral could make its way back through the load to the phases. Closing the CB A2-3 Tie to provide service to panel A1 and A2 should not be an issue, right? Thanks again!

I thought the same thing for a minute but realized the 120VAC reading is phase to phase across the tie breaker. no neutral readings involved. The phases on the line side of tie are completely isolated and are not grounded obviously.

UPS's are in bypass mode. Not being used. See breaker Open/closed breaker status.

Can anyone suggest possibilities of why we are reading 120vAC across CB A2-3 TIE on the attached one-line diagram? All breakers are closed unless indicated w/ "open". Readings were taken at VM1 and VM2 as shown on one-line. VM1 readings were 120vAC across the line side and load side of CB A2-3...

@che12345 "...The source can only supply distorted voltage and voltage alone doesn't heat anything. Distorted current flow does. If the 20A has a decent amount of higher frequency harmonics then it could be causing the breakers to heat up. 20A of 60hz should not". @WAROSS The 18% current...

I'd like to add that these rectifier cabinets were brand new from Factory and were being installed by the manufacturer in a week long outage. The new rectifier cabinets were to replace a working but obsolete system. The system was powered up after installation but never commissioned due to the...

We have two 1600A adjacent feeder circuit breakers(CBA3 and CBA4)on a rooftop substation. Both CBA3 and CBA4 feed busducts BD3 and BD4 respectively. Last night CBA4 opened on an Instantaneous fault of 7kA. All loads off of CBA4 were de-energized as expected. However, we also found that a machine...

Thank you jghrist! That's the solution for this application.

That's too bad. Sounded like a good opportunity to reduce feeder side Arc Flash IE. Good Luck and thanks again for the reply.

Unclebob, Thanks for the insight. I'm sure the insulated barriers will be a cost effective AF mitigation technique vs. MV breakers or other expensive methods. I'd love to see some before and after pictures upon completion of the barrier install. Thanks again!

Thank you Dave. That's our current analysis strategy, but wanted a reality check to make certain there wasn't a more scientific approach to isolation and barriers. Thanks for your response!

When can an Arc Flash propogate from the feeder bus of a panel to the line side of the Main? What constitutes a barrier between the Main section and a feeder section of a distribution panel? I'm curious how other firms deal with these questions. It's real easy for the Arc Flash firm to just...

I've seen this done many times, but is this method acceptable for installing additional cables to an already full transformer secondary spade bushing?

These motors are all outside and are driving vertical pumps for a cooling tower. Each motor is fed with 3-350cu. in 2-1/2" Rigid Steel conduit. Each conduit is routed overhead on pipe racks 20+ feet above ground and into a building that houses the MCC. Is it possible that these motors were...

waross, I hope I understand your question correctly, but the panel SCCR is not based on the Available Short Circuit Current. The panel OEM had know idea what the Available Short Circuit Current would be when designing the enclosure.

Thank you juleselec. So, in the IEC world, you would assume the peak rating of the subject panel is 5kA(rms) x 2.6 = 13kA?

Thank you jraef! I know it sounds obvious, but I needed someone else to confirm that "like" current units should be compared.