AC Electical Question

DaveNH · Feb 12, 2004

Knowing very little about AC I need to ask.

I have some telcomm equipment power by an AC power strip with six outlets.
The strip is powered from an AC/DC inverter.
The are five pieces of equipment powered from the AC power strip.
(The sixth outlet is empty.)
Customer wants to move off of the existing inverter -both AC and DC over to the new one I just installed.

Customer still wants/needs to use the power strip.

Can I make a cheater cord and back feed AC into the sixth outlet
of the AC power strip and then move the main feed of the power strip to the new outlet?

The two circuits (old AC and new AC) both come from the same power panel but are on different sides of the panel. (CB 9 New -- CB 10 Old)
Panel is labled 208 volts. I'm think there maybe a phase difference between the left and right side of the power panel (????)

MossRoad · Feb 12, 2004

I guess I don't understand why you would want to do this. Sounds dangerous, illegal and will almost surely void any insurance claims should there be a fire. And you would be liable for all damages.

jinman · Feb 12, 2004

( The strip is powered from an AC/DC inverter. )

Dave, some things are not "stacking up" correctly in your description. You mention the "AC/DC Inverter" but you never say where the DC is coming from that you are inverting. This makes me think you are talking about a UPS (uninterruptible power supply) rather than an inverter. From what you said, you'd be mixing some AC and DC in the same power stip and thats a big, big NO-NO. I think that's why Mossroad was so strong in his response too. /forums/images/graemlins/confused.gif

slowrev · Feb 12, 2004

I agree with everyone else on this subject so far. Not real sure what you are trying to do but I suspect the results could be dramatic and unsafe.

heehaw · Feb 12, 2004

if you try it, make sure someone has a video camera on at the time, you may be able to win one of those funniest/scariest home videos.
heehaw

DaveNH · Feb 12, 2004

Ok, I'll try to claify.

I have some telcomm equipment power by an AC power strip with six outlets.
(Just like the one you probable have under your desk, you plug it into the wall and now you have six AC outlet.)

The strip is powered from an AC/DC inverter.
(The Inverter is fed by both an AC source and a DC source (big string of big batteries making -48 volts DC. If AC fails, the inverter changes the DC to AC and keeps the AC powered equipment happy. When AC comes back, the inverter switches back to commercial AC. The inverter has only one output - 115 VAC it's like a UPS only bigger (higher KV and a hell of a lot fast.)

The are five pieces of equipment powered from the AC power strip.
(The sixth outlet is empty.)

Customer wants to move off of the existing inverter -both AC and DC over to the new one I just installed.
(I installed a bigger inverter so the customer is giving back the AC feeds and the DC feeds from the inverter he is using now)

Customer still wants/needs to use the power strip.
(We only provided two new AC outlets to the customer)

Can I make a cheater cord and back feed AC into the sixth outlet
of the AC power strip and then move the main feed of the power strip to the new outlet?

( A small extension cord with male plugs on both ends, wired hot to hot, neutral to neutral, ground to ground. Plug one end into one of the new customer outlets and then other end into the sixth (empty) outlet on the power strip. Then remove the AC cord from the customers old AC outlets.)

The two circuits (old AC and new AC) both come from the same power panel but are on different sides of the panel. (CB 9 New -- CB 10 Old)

(The AC that is powering the strip now is coming from a power panel CB 10 right side and the new service will be on the left side of the power panel. )

So, thinking about this....
I guess my real question is:

Is there a phase difference between the left side of a AC Power panel and the right side of a AC power panel?

DaveNH · Feb 12, 2004

Guess you missed the one where I put a ladder up against a swing set, climbed up to catch a swarm of bees in a near by tree, took one step to many, started to go,
grabed the branch and we all came tumbling down /forums/images/graemlins/blush.gif

PineRidge · Feb 12, 2004

Sounds to me like you are tying to make a temporary connection so that you don't have to power down your equipment. Are you aware that in a main circuit panel you have 110 volts on the left side of the box and 110 volts on the right side of the box but both legs together is 220 volts?

Inspector507 · Feb 12, 2004

Then remove the AC cord from the customers old AC outlets.)



That will leave the unused male cord end laying on the floor?? That thing will be hot.
Everything you're wanting to do, would not be something I would want todo.
2 male cord ends are dangerous just to start with.
You've got a 33% chance of them being on the same phase in a 120/208 panel. On a 3 phase panel, the pahses aloternate ABCABC....etc on the right and ABCABC on the left.
Doesn't sound like a safe set-up at all

DaveNH · Feb 12, 2004

Thanks Mike.
You are correct, we want to keep the telcomm equipment running.
You are correct, I'd end up smoking the telcomm equipment.
Some reason I got hung on finding out about a phase difference
and overlooked the total combined voltage. /forums/images/graemlins/blush.gif Thank you! /forums/images/graemlins/grin.gif

I realize the point is moot because of the location of the breakers
but in theory, if both breakers where on the same leg, think it would have worked?

DaveNH · Feb 12, 2004

"That will leave the unused male cord end laying on the floor??"

No, I thought I'd stick that into the customer's second outlet and then remove
my cheater cord.

MossRoad · Feb 12, 2004

Sorry to sound so terse.

Is what you are trying to say; "I want to keep some equipment running while I change the source supplies. How do I do that?"

If so, I don't know.

PineRidge · Feb 12, 2004

I realize the point is moot because of the location of the breakers
but in theory, if both breakers where on the same leg, think it would have worked?


So you have this power strip that is already energized by a breaker on the left side of the main panel. And before you disconnect you want to power it by a breaker on the right side of the panel box by using a male plug end inserted into the power strip, correct? This would be a temp thing so that you could quickly make your change over.

Any way of moving breakers so that you would pick up power on the SAME side of the main panel box? In that instance it would still be 110 volts.

Maybe Inspector507 will chime in here with some expert advice on what you are needing to do to make it legit. /forums/images/graemlins/grin.gif

heehaw · Feb 13, 2004

i guess i missed that one, but your description leaves a dandy picture in my head....hope you didn't get hurt, but how many stings did you get out of that trip?
heehaw

PBMAX · Feb 13, 2004

Just because they are on the same phase does not mean it will not trip the breaker.
I have seen 2 circuits on the same phase trip a breaker if they are on the same exact wire for neutral..

I suggest you find a way to back up the info on the equipment just incase, if you ever do try this...

As others have stated I would not ever recommed you back feed in such a way. YOu could wind up with some serioius FIRE WORKS /forums/images/graemlins/blush.gif

RET · Feb 14, 2004

OK, since this is now a brain teaser just for fun and we ain't gonna really go do it...

Before we start this job, the equip. is running on grid AC. Batteries are fully charged and ready to kick in if needed.
Let's push a button on the inverter that tells it to swap to DC source. No problem. We're now running off of batteries (I hope someone checked the battery charge before we started this!).
With the equip. feeding from batteries....we should have at least 30 minutes to go to the breaker box and do some wire/breaker moving to make this transition work. Maybe there's even a way we can get around even having to do that?

OK, somebody else finish this story now....I'm getting myself confused. I thought of the ideal of swapping to DC....somebody else take it from here and provide the next step. It's past my bedtime.

OkeeDon · Feb 14, 2004

I thought of disconnecting the inverters from the AC power and using the battery power also, which would eliminate any phase problems, and started to write such an answer, but then I came right back to the backfeed. I just don't know what happens when you feed power from two different sources into two different ends of the same power strip. And, I don't want to experiment to find out... /forums/images/graemlins/shocked.gif

DaveNH · Feb 14, 2004

Sorry to have caused any one a head ache.

But the equipment is only AC powered, even when on batteries.
The inverter's output is only AC. So shutting down commercial
or the batteries, still leaves me with having to move an AC plug. /forums/images/graemlins/confused.gif

I thought there maybe a way around it but I don't see now. /forums/images/graemlins/crazy.gif

Telecomm folks (and IT) are really picky and don't ever want to see the equipment powered down. There's the fear that it won't come back up.
Just imagine if TBN went down for a few hours, folks sure would be upset. /forums/images/graemlins/blush.gif

Gomez · Feb 15, 2004

Is the equipment capable of dual power supplies? I am currently working on a project involving upgrading some Cisco switches in an office building. The new switches will have an AC and a DC supply. During normal operation, both supplies share the load. If the AC fails, the DC fed supply will carry the switch, and vice versa. The DC source is a battery backed system, similar to a UPS without the double conversion. Initially, the IT group wanted to install a UPS on each switch. After some investigation, we found this solution to be preferable to UPSs and their associated maintenance.