Problem with Temporary Power to Subpanel

[Tom in Seattle]

I'm going to replace my main SE panel a bit later and along with that upgrade I will have a 100A subpanel in the garage attic. I've installed the subpanel and wired all the new circuits. It will eventually get fed with #3 THHN from a 100A breaker in the new SE panel.

One of the circuits I wired in the subpanel powers interconnected heat, smoke and CO detectors. Before wiring this into the subpanel it was temporarily powered by an unused circuit from the old main panel. I'd like to keep this powered during the remodeling.

Since the new circuit attaches to the right bus bar I figured I could hook the hot wire from the old unused circuit to the right bus bar lug and the neutral to the neutral bus, and then turn on the smoke detector circuit breaker. A voltage sensor shows there is voltage on the bus, but when I turn on the breaker for the smoke detector circuit, it's not getting any power. Any idea why?

Since I'm using QO breakers my plan now is to connect the old circuit hot wire directly to the breaker since it accepts two wires. This would effectively splice them together inside the subpanel and still maintain protection via the old circuit breaker. I'm just curious why connecting to the bus did not work.

Thanks.

 

[pattenp]

The breaker for the detectors is not on the same side you have power to. The buss jumps back and forth down the breakers. In other words all the breakers on the right side are not getting power from the right hand buss.

 

[Tom in Seattle]

The breaker for the detectors is not on the same side you have power to. The buss jumps back and forth down the breakers. In other words all the breakers on the right side are not getting power from the right hand buss.

I'm well aware of that. This was the 4th single pole breaker on the left side from the top, which puts it on the right side where I had power connected.

 

[pattenp]

Based on the info you've given I have no clue as to why you don't have power.

What type of voltage sensor are you using to check that there is voltage. You should be using a multimeter with putting a prob on the hot and a prob on the neutral. Not one of the inductive non-contact light sticks.

 

[Tom in Seattle]

What type of voltage sensor are you using to check that there is voltage.

I was using the non-contact type sensor. I have a multi-meter I can use.

 

[pattenp]

The reason I said not to use the non-contact type was that sometimes they indicate voltage even though you may not have full voltage.

 

[Norcal]

I was using the non-contact type sensor. I have a multi-meter I can use.

IMO those are in most cases,just a toy.

 

[Tom in Seattle]

Mystery solved On a QO panel what appears to be is not necessarily the case. Looking at the bus bar connections for the individual breakers does not tell the whole story. Using a VOM reveals the secret: the right and left side attachment lugs "swap positions" internally within the main breaker, so the left side lug attaches to the right side bus bar and the right side lug attaches to the left side bus bar.

 

[pattenp]

You're welcome.

Mystery solved On a QO panel what appears to be is not necessarily the case. Looking at the bus bar connections for the individual breakers does not tell the whole story. Using a VOM reveals the secret: the right and left side attachment lugs "swap positions" internally within the main breaker, so the left side lug attaches to the right side bus bar and the right side lug attaches to the left side bus bar.