Transfer switch question

[tallgirl]

During a recent conversation about some power management glarp I've been working on, I had a question about transfer switches that I couldn't answer and couldn't find an answer for anywhere. I'm going to give me as an example, but I'm not going to run out and do this ...

As y'all may remember, I've gotten into this "Solar Power" thing and I've been working with some people on renewable energy issues. One thing that comes up is the difference between running AC inverters through a "critical loads" panel (just the stuff you want during a power outage) and what I've done, which is oversize the inverters so I can run my house on batteries.

In my case, I know from a huge amount of data logging that my peak current is about 30A per leg for a 60A subpanel. It's 27A on the A leg and 31A on the B leg. I could even tell you the exact second that happen, but I digress.

The hardware I personally have a 50A output limit. I knew people who've run air conditioning on identical equipment, but it seems both stupid and a waste of batteries. But for the sake of discussion, let's assume I wanted to have an air conditioning condensor on a transfer switch so that normally the condensor is fed directly from the utility, but if it's hot, miserable, and I wanted to run the A/C on batteries, I'd just flip the transfer switch (so this is obviously a manual switch) and that would be that. What is the code section that would even cover such a thing? Is it the usual "Separately Derived Power" parts of the code?

 

[ron]

Article 702

 

[tallgirl]

Article 702

I read 702 and it doesn't appear to apply.

The two power sources are both normally active, except when the PoCo goes away. So it isn't the case of the PoCo and a standby generator it's the PoCo and a separately derived system that is typically synchronized with the PoCo.

In particular, 702.5 and 702.6 are what I'm curious about.

702.5 says I can select what gets connected, by which I assume it means that if I have this "alternate power source" connected, and it's current limited at, say, 30A continuous and 50A for 60 seconds, it can connect to a 200A service panel, so long as the "user" knows they best not turn on more than 30A worth of loads?

What bugs me about 702.6 is that these are typically two in-phase supplies, where the inverters (it's all about inverters) lock onto the PoCo's power and keeps that same frequency. So this seems a bit more like Article 705, perhaps?

 

[quogueelectric]

I read 702 and it doesn't appear to apply.

The two power sources are both normally active, except when the PoCo goes away. So it isn't the case of the PoCo and a standby generator it's the PoCo and a separately derived system that is typically synchronized with the PoCo.

In particular, 702.5 and 702.6 are what I'm curious about.

702.5 says I can select what gets connected, by which I assume it means that if I have this "alternate power source" connected, and it's current limited at, say, 30A continuous and 50A for 60 seconds, it can connect to a 200A service panel, so long as the "user" knows they best not turn on more than 30A worth of loads?

What bugs me about 702.6 is that these are typically two in-phase supplies, where the inverters (it's all about inverters) lock onto the PoCo's power and keeps that same frequency. So this seems a bit more like Article 705, perhaps?

I feel it is always best to make it idiotproof for the customer so they cannot possibly backfeed the poco look at the gentran systems. This would also be good for your inverter transfer because you can manualy transfer whatever load individually ckt by ckt to the alternate source. If you only wanted ac load or doorbell there are 10 cks generally on the panels I normally install and you can pick them up on ebay fairly cheap if you need to. Or you can pay retail which just couldnt do.:grin:

 

[iaov]

EMERGEN Makes a relatively inexpensive panel also that allows you to manualy select wich loads you want on. They have watt meters so you can balance the phases.

 

[ron]

After reading 702.1 and 702.2, it would seem that I would still apply your situation to 702. Your supplies are permanent and you wish to use one as standby.
702.5 essentially says in the 2005 edition that the standby source does not need to match the size of the normal source (as you mentioned).
702.6 says that you can't put the two sources in parallel unless you go to 705.
705.1 seems to indicate in the scope that the sources are in parallel only.

 

[tallgirl]

After reading 702.1 and 702.2, it would seem that I would still apply your situation to 702. Your supplies are permanent and you wish to use one as standby.
702.5 essentially says in the 2005 edition that the standby source does not need to match the size of the normal source (as you mentioned).
702.6 says that you can't put the two sources in parallel unless you go to 705.
705.1 seems to indicate in the scope that the sources are in parallel only.

Thanks. I think the answer is in 702 or 705 somewhere. I'll be back when I have more questions