Voltage drop

[Nelatieh]

Mike, I am a residential electrician, I use a contractor license to work in Pa.
I worked overseas in crazy poor areas.
I studied 2 years in the USA to learn the codes.
On top of my degree from a French technical school overseas.
One of my customers has a large commercial building, he has 208/120 panels and 277 panels,
He asked me to add an outlet in a large closet space.
I tapped into a 120 outlet that was there
Parallel using MC 12/2 7-8 feet long max.
He plugged an Ethernet transfer switch 4.0 amp.
Half the lights in that place flickered and we had a voltage drop of 8 volt after loading the circuit with the switch.
Plug a 50 watt chip light and the drop is 18 volt.
Hot to ground stayed 122.
The lights are all on the 277 circuits not on the 120
It is a 20000 square foot open building used for pickle ball.
I did tell him to get a commercial electrician.
Any thoughts ?
Thank you

 

[ptonsparky]

IMO, the issue was there before your new receptacle went in. This should not have affected the lighting in any way unless they are controlled/dimmable and that portion uses 120 volt.

Hot to Equipment Ground was 122. What was the Neutral to Equipment Ground voltage?

 

[roger]

What does "Parallel using MC 12/2" mean?

 

[Nelatieh]

IMO, the issue was there before your new receptacle went in. This should not have affected the lighting in any way unless they are controlled/dimmable and that portion uses 120 volt.

Hot to Equipment Ground was 122. What was the Neutral to Equipment Ground voltage?

It was dropping by 8-10 volt every time we add a load
Outlet had a blink camera on it and tested 122 volt that’s why we used it.

 

[Nelatieh]

What does "Parallel using MC 12/2" mean?

Sorry English is my third language.
We just added an outlet hot to hot neutral to neutral and green to green, in a parallel way.

 

[Strathead]

It was dropping by 8-10 volt every time we add a load
Outlet had a blink camera on it and tested 122 volt that’s why we used it.

neutral should have zero volts on it plus or minus a minute amount. That you have voltage on it means your neutral to ground bond isn't in place properly, for that system (likely a 480 to 120 transformer.) My immediate instinct is that isn't the cause of your problem though.

 

[Space]

It was dropping by 8-10 volt every time we add a load
Outlet had a blink camera on it and tested 122 volt that’s why we used it.

It doesn't appear like you answered his question. What is the neutral to ground voltage on the 120V outlet?

It sounds like there is a high resistance in series somewhere that is causing voltage drop as current increases. I would suspect a loose/corroded connection.

 

[garbo]

Side note on my dukes of hazard home state of Pa. Politicians in Harrisburg have been talking about enacting a state wide electrical license since my dad had to take the city of Philadelphia electrical contractors test 60 years ago (1964). Great Philly IAEI sent people up to the state capital about ten years ago to attempt to get a state license. A few politicians promised to look into it. Worse part of not having a state license some towns do not recognise any other electrical licenses and make you jump thru hoops having to take a 4 hour test then usually two trips. Worse was a tiny 2 square mile town where the person issuing license was the only electrical contractor in the hick town then attempted to fail me after my inspector passed the job. Gave him the NEC article that allowed me to make the one & only #14 guage splice that I made in a replacement panel. Told me he would let me get away with it that time.