Transfer Switch

[Gunnar Alquist]

Country property. A backup portable generator is temporarily connected to a panel that controls a limited number of circuits in a home. Clearly, they don't want to purchase a huge generator for intermittent use. Typical backup generator scenario in my area. Intended for a day or two while the power is out.


The transfer switch was unusual (for me). This involved two double-pole circuit breakers installed back-to-back with a mechanical link that will only allow one breaker to be "on". Ok, so that is how a transfer switch should work - it will isolate the panel from the utility (disconnect from PG&E) in favor of the generator or will connect to the utility and disconnect from the generator. But, I normally see a separate transfer switch box, not this mechanical device between breakers.


So (finally), my question is: Is this an approved transfer switching method? It doesn't look jury-rigged. It looks like a device manufactured specifically to be used as a transfer switch. I just have not seen this before.

[Jim Port]

Does this only serve the few circuits in the lower part of the panel? If so I don't see an issue and there is no interconnect between the utility and generator.

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Does this only serve the few circuits in the lower part of the panel? If so I don't see an issue and there is no interconnect between the utility and generator.

[Gunnar Alquist]

Does this only serve the few circuits in the lower part of the panel? If so I don't see an issue and there is no interconnect between the utility and generator.

Thanks for replying Jim,

Yes, a feed was run from a 50 amp breaker at the service equipment to one side of that strange doubled-up breaker setup in this panel (the generator feed ran to the matching breaker). These few branch circuit wires were protected by breakers in this panel, then run back and spliced in to the original conductors at the service equipment. The neutral and equipment grounds never left the service equipment.

I run into backup generators and transfer switches fairly regularly. The thing is that I often see permanent backup generators setup with automatic transfer switches that detect a power outage, kick on the generator and flip the transfer switch. When a portable generator is used, I either see a dedicated transfer switch in its own box (like a knife switch) or I see it done way wrong with labels that say "turn this one off" and "turn this one on". :shocked: Oy!

I was mainly asking if this was an "approved" setup rather than something jury-rigged. It looked like a manufactured device specifically for this use. But, I have not seen one of these before.

[Lon Henderson]

My initial reaction is ... I like that and I'm going to look into doing that at my house.

[John Kogel]

Ditto, that setup is legit so long as the loads in that panel do not exceed the max provided by the feeder and the breaker in the main panel.

There is another style I have seen where a large panel board has a split buss with the lower end controlled by a manual transfer switch.

[Jerry Peck]

Gunnar,

Do you have a better photo of that MTS label?

That may very well be a listed device, but I can't tell by that photo, and I couldn't find a similar manual transfer switch with a Google search.

First appearances is that it looks okay, load management may be an issue, something you might want to point out (the 50 amp main and feeder capacity to that panel is being replaced by a 30 amp ... it is likely that not all circuits will be working on the emergency generator supply.

A bigger issue may be the neutrals (lack of) for the 120 volt circuits going from that panel back to where they are spliced - the circuit neutrals need to run with the circuit hot conductors wherever the circuit hot conductors go. That flexible metal raceway may get a bit warm from the eddy currents with no neutrals run with the hot conductors.

Of course, though, that may likely require a larger raceway as the number of conductors will increase.

[Gunnar Alquist]

Hi Jerry,

I do not have a better pic of the label. Sometimes I remember to take label specific pics and sometimes I don't . I will try to remember to take more specific pics in the future.

I ended up deferring on this. Primarily because researching this type of system could take a couple of hours. Really beyond the scope of a regular home inspection.

[Richard Duncan]

Here is a link to the mechanical type lockout.

http://www.interlockkit.com/

[david shapiro]

Here is a link to the mechanical type lockout.

http://www.interlockkit.com/
Something seems a little funny about that, Richard.
There's nothing wrong with Met Labs, from anything I've seen or heard.
However, the fact that they specify compliance with UL 67, the standard for panelboards, only with regard to installation and mechanical operation, makes me wonder what the device's classification doesn't cover.
Usually, if something such as a CB is classified for use in panelboard X, this means that it's operating characteristics are equivalent to or at least compatible with what's in the panel, just as much as the items listed in the panel alongside the schematic and ratings.

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Here is a link to the mechanical type lockout.

http://www.interlockkit.com/
Something seems a little funny about that, Richard.
There's nothing wrong with Met Labs, from anything I've seen or heard.
However, the fact that they specify compliance with UL 67, the standard for panelboards, only with regard to installation and mechanical operation, makes me wonder what the device's classification doesn't cover.
Usually, if something such as a CB is classified for use in panelboard X, this means that it's operating characteristics are equivalent to or at least compatible with what's in the panel, just as much as the items listed in the panel alongside the schematic and ratings.

[Jerry Peck]

Did they make the breaker?

I would think that the breaker would already be a listed item.

[Richard Duncan]

Did they make the breaker?

I would think that the breaker would already be a listed item.


Only the mechanical lock-out device.

[Jerry Peck]

As an inspector, my question to the contractor would be this: provide a letter from the manufacturer of the panelboard stating that this device does not negatively affect their panelboard.

That's like my solution for damaged trusses:
- Step One: Get an engineer's letter stating what needs to be done.
- Step Two: Get an engineer's letter stating that what needed to be done was actually done.

[david shapiro]

As an inspector, my question to the contractor would be this: provide a letter from the manufacturer of the panelboard stating that this device does not negatively affect their panelboard.

That's like my solution for damaged trusses:
- Step One: Get an engineer's letter stating what needs to be done.
- Step Two: Get an engineer's letter stating that what needed to be done was actually done.
In one way it is, in one way it isn't:

The engineer is motivated by being hired to write the first letter, and motivated by being hired to re-evaluate, and seeing that his specs were met, to write the second.
I don't see what would necessarily motivate the panelboard manufacturer to sign off on some other manufacturer's product.

[Jerry Peck]

I don't see what would necessarily motivate the panelboard manufacturer to sign off on some other manufacturer's product.

Precisely ... the panelboard is listed without that in there.

The manufacturer of the panelboard would likely want to know how it's panelboard was modified.

[Gunnar Alquist]

Thanks Richard, David and Jerry,

I had not even thought about the brand compatibility and approval issue. I am going to bring these pics and your observations to my next chapter meeting. Should be interesting.

[John Kogel]

How is the manual transfer switch different from any automatic switching device, such as those you are used to seeing?

The transfer switches we see here, just as many manual as automatic, appear to be manufactured by the major companies, Schneder, Generac, or Kohler. Any violations would be in incorrect installation, IMO.

This is from the GE installation manual.
"The InterLock Kit will only allow one of these breakers to be in the “ON” position meeting the requirements of Article 702 of the National Electric Code ANSI/NFPA 70. The installation of the breaker retaining strap meets Article 408.36 (NEC 2008). "

[david shapiro]

How is the manual transfer switch different from any automatic switching device, such as those you are used to seeing?

The transfer switches we see here, just as many manual as automatic, appear to be manufactured by the major companies, Schneder, Generac, or Kohler. Any violations would be in incorrect installation, IMO.

This is from the GE installation manual.
"The InterLock Kit will only allow one of these breakers to be in the “ON” position meeting the requirements of Article 702 of the National Electric Code ANSI/NFPA 70. The installation of the breaker retaining strap meets Article 408.36 (NEC 2008). "



The devil's in the fine print. If I saw a Schneider device mounted on a Square D panel, I would expect it to be fully compatible, but even so I might check with Schneider. If it was a GE device, I might not expect Schneider to be as forthcoming about its suitability for use with their panel. Sometimes legalese seems to just be precision, but when I see "Classified as suitable only with respect to," or whatever the words Gunnar read were, I want to check. Because I'm ignorant.