Two 15A Circuits = One 30A Circuit? (1 Viewer)

[JeffreyS]

I'm building my first HT. I just purchased an APC Smart-UPS 3000 on eBay for $385 shipped. Short outages (less than one minute) are common where I live, so having my entire HT behind a true-sine UPS will be a Very Good Thing.

This UPS has a NEMA L5-30P plug, so I would assume it wants a 30A circuit to feed it. An electrician is already coming this week to inspect my house wiring and correct some miswired outlets; I could have him set up a 30A dedicated circuit for me as well.

But do I need to do that? I only know enough about electricity to be dangerous , but it seems that it would be easy to combine two 15A circuits into one 30A supply. I'd just have a L5-30R receptacle with two 5-15P power cords screwed to its terminals. Each 5-15P would plug into a different dedicated 15A circuit.

As long as the frequency and phase of the AC is the same (which it is, since both 15A circuits come from the same breaker box), is there any reason why I wouldn't want to do this? Other than ensuring I actually use two different 15A circuits, is there anything to watch out for?

 

[Gary Silverman]

Jeffery, you're right, you do know enough to be dangerous. Have your electrician run a 30 amp/120 volt circuit. But, if you want to give him a good laugh, tell him your idea.
Seriously, paralleling 2 circuits like this could be dangerous and is prohibited by the NEC as well.
Just a couple of thoughts. If there was a problem, and the breakers needed to trip,one might trip and the other one might not trip at the same time, leaving the problem there. When a breaker needs to trip, you want it happen fast! And if someone needed to work on the circuit, he may turn off one of the breakers, not realizing that the circuit is still hot.

 

[Jason.Soko]

What in gods name are you going to do with 30amps !!

 

[JeffreyS]

Thanks Gary, I had a feeling there would be something very wrong with the idea...

Jason, my equipment's total listed wattage is 1815W. APC says the SU3000's maximum load is 2250W. Though I know my equipment will most likely never pull the full 1815W, I want some room for future expansion. The SU3000 has a 30A plug, so I figure it needs a 30A circuit.

Hey, the SU3000 was only $300; how can one pass up a deal like that!?

 

[Jason.Soko]

Jeff,

I've seen full surround sytems, with player, plasma tv and mcintosh amplifiers playing at VERY high levels pulling at a max of 6-7amps. If you actually draw anywhere close to 30amps you have worse things to worry about.

 

[Chu Gai]

That's a ballsy looking device. Jason, it requires a 30 amp circuit because that's what APC says it does. I'd imagine a lot of the reasoning has to do with the size of the battery that's in there.
The only thing I've got a question about is why that link you provided states that it meets UL 1449 and doesn't say 'meets UL 1449 2nd edition'. Maybe they mean the same thing, but the latter is an upgraded specification. Good price though.

 

[JeffreyS]

Ok, I have another crazy idea. In this episode, I will have the electrician wire the 30A circuit to an outlet right by the breaker box. Then, two existing 15A circuits to the HT room will be plugged into the UPS and not the breaker box. This would give me two battery-backed outlets in my HT room while keeping that big ugly white (and possibly noisy) UPS box out of it. I'd put my PA on one outlet, and everything else on the other.

Yes, I know not to plug in surge suppressors behind the UPS.

The wall outlets in my employer's data center are UPS-backed, so I know my idea can be done somehow.

 

[Chu Gai]

Well the ideal place for a surge suppressor, and not those Panamax and Monster types, is at either the panel or the meter outside. Whole house ones can be fairly inexpensive and if you're having the electrician there anyways, it shouldn't take more than a few minutes of his time. Think about it.
I'd imagine that your approach would work and the electrician will run things according to code.

 

[Cary_H]

There's a similar thread running elsewhere.
My question is why would you want a UPS on your system? Battery back-up units and line conditioners almost always offer surge protection as well, which is a must, but the three are different animals altogether.
I suppose the confusion stems from many of the units out there offering more than just one capability. Generally speaking, the variance between the asking prices of these rigs are a pretty fair indication of what each of them can give you.
I concur with a couple of previous posts. If you have the choice, the best place to put surge protection is as close to where the service comes into your home as you can.
Back to the circuit question....I'm confused. If you are able to pull 2 12 ga. strands, why not just pull a couple more with them if you might want them later? You can leave them in the wall at one end and not connect them at the panel. Bring them into play once the need arises.

 

[Cary_H]

Jeffery...what your employer is doing and what you propose are not quite the same.
If the data center is of a critical nature, the outlet in the wall that you refer to will be tied into an emergency generator that will pick up the system's load if the power in the area goes out. For the short period of time between this generator coming on line after the power loss, a UPS picks up the load so the system doesn't crash.
The capacity of the UPS will be sized to the appetite of the system. The more critical the system, the longer it'll be designed to cope.
I used to work where a well known phone carrier housed a main hub. They had a mucho dinero, enormous, state of the art backup system of batteries tied to rectifiers to keep them running in an outage. The best they could do was about 3 hours tops if both generators failed to start.
I'd give your home unit about the time it'll take for you to grab the remote and shut everything off. That's why the UPS idea is pretty much pointless.

 

[Simon Ngan]

Oh my goodness, I'm almost ready to get the SmartUPS 1000VA and it costs $650 Canadian here brand new. The beast looks bulky and nice

One thing I'm concern about the SmartUPS is, does it actually draw more power than let say, the cheaper version BackUPS? Would the SmartUPS always consume 1000VA no matter what the load is because it's feeding through the batteries?

Thanks,

Simon

 

[Cary_H]

The VA rating relates to the capacity of the unit's battery. The draw on the unit will be whatever load the devices connected to it's backed up outlets ask of it.
The less the draw, the longer the time the unit will keep you running in the event you experience a power outage.
You size your purchase based on your system's needs and the time you'd like to have in reserve.


The "Smart" designation APC uses refers to a software package that can perform an orderly shutdown of your system in your absence if the power was to go out.
You connect the UPS to a port on your PC, install the program and run it in the background.

 

[JeffreyS]

Cary_H said:

what your employer is doing and what you propose are not quite the same ... emergency generator that will pick up the system's load if the power in the area goes out

In my case, they are the same. There's a big UPS and no generator. I wouldn't call this data center super-critical, either. If it's down for a few hours, it would surely not be a good thing, but in this specific case it is less expensive than having a generator system.

 

[JeffreyS]

Simon said

One thing I'm concern about the SmartUPS is, does it actually draw more power than let say, the cheaper version BackUPS?

First of all, It has been documented in these forums and elsewhere that you shouldn't use the cheaper Back-UPS (or similar) units in a HT system; the electricity they output has a 'stepped' sine waveform, which tends to work with computers but is not optimal for HT gear. It is better to use a UPS that produces a true sine waveform. According to my recent research, most UPS manufacturers' high-end desktop or rackmount UPSs (including most of APC's SmartUPS line) are true-sine. These models also seem to mostly be line-interactive UPSs, which means they also provide the voltage regulation feature that you'd get with a decent line conditioner.

As far as the maximum power the Smart-UPS itself draws from your electrical mains, you should be able to find that on APC's web site.

 

[Cary_H]

JefferyS;

Sounds fair enough to me, Jeff.
If I may play devil's advocate here however, I'm not sure I'd want to have my stuff plugged in, nevermind up and running with anything resembling a thunderstorm outside.

 

[nolesrule]

If I may play devil's advocate here however, I'm not sure I'd want to have my stuff plugged in, nevermind up and running with anything resembling a thunderstorm outside.

Good thing you don't live in Florida, or you'd never be able to use your equipment for 7-8 months out of the year. Lately, we've had long thunderstorms 2, 3 and even 4 times a day.