Air conditioner disconnect for inverter?

jaggedben

Senior Member
So it was recently brought to my attention that this type of disconnect is insanely cheap compared to what we've been using to comply with the grouped disconnect requirement when an inverter is not near the point of interconnection. 690.15 in the 2014 NEC. The safety switch has always been what I've seen in the solar industry, and I've always just done what was done before. But there's a lot of money to be saved here, so I'm asking myself, if it's good enough for the air conditioning guys, why not good enough for solar inverters?

(Before anything else: this thread does not pertain to disconnects required by utilities. Just NEC requirements.)

Anybody using these? (for small inverters, up to 48A output)
Anyone aware of a good reason not to use them?

Thoughts:

First, 705.22 includes:
" the disconnecting means shall consist of ... switch(es) or circuit breaker(s) with the following [feature]:
...
(2) Externally operable without exposing the operator to live parts...
It seems like perhaps this rules out a pull-out type disconnect, but we'll always have another disconnect that can comply with 705.12. This is just to comply with 690.15. (Also, is there a good reason that 705 should rule out pull out disconnects?)

Second, the 2017 NEC changes things up quite a bit in 690. We now have similar language as above in 690.15(D), except it says "externally operable without exposing the operator to contact with energized parts..." (emphasis added). It also includes "A load break fused pull out switch" among the list of options for an 'equipment disconnecting means'. I find this, er, interesting. First, why must the pull out switch be fused? Second, if a type of pull out switch is allowed, then do pull out switches not expose the operator to live parts? Or does a pull out switch "expose the operator to live parts" but not expose them "to contact with energized parts"?

Does this language about exposure to live parts appear in any non-solar related requirements for disconnects elsewhere in the code?

Opinions and thoughts appreciated.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Not sure about solar usage, but I have even used the el cheapo disco on a house as a remotely-placed residential generator disconnect.
 

MAC702

Senior Member
Location
Clark County, NV
As an HVAC guy who the uses or installs the cheap disconnects everyday, but knowing nothing about the PV world beyond studying for one hour and passing the state installer exam, my first question is how often will you need to use the disconnect, and how often will that be under load?

In the HVAC world it is only needed during maintenance, and will rarely be pulled out under load. I don't know what difference that makes to you.
 

jaggedben

Senior Member
...

In the HVAC world it is only needed during maintenance, and will rarely be pulled out under load. I don't know what difference that makes to you.
Pretty much the same deal for solar inverters, I think, if by 'rarely' you mean that once a unit is installed and commissioned, most are not touched again for a long time. (Or do you mean that most of the time that you yourself operate one, you have the circuit turned off elsewhere?) Also since inverters don't restart immediately when reconnected, it's only disconnecting that one needs to be concerned with load. But these things are load break rated anyway, right?
 

Adamjamma

Senior Member
I was actually considering using these in kitchens in Jamaica where one hardly ever has an electric stove but needs to wire for one anyway... just in case.. yet is stuck with inspectors arguing that the disconnect needs to be in the kitchen... but so far have gotten by with using the DP switch from the UK...
 

StarCat

Senior Member
Location
Moab, UT USA
The no way AC Mans Disconnect

The no way AC Mans Disconnect

I have to tell you as an HVACR guy, I despise those disconnects for several reasons....
1.They are knuckle busters
2.They can cause overloads if you do not stab them perfectly and quickly on a system that has the contactor already engaged
You are correct, they are the CHEAP AC mans favorite, but in real terms just make things more difficult. I consider them the hallmark of a bad install.
While somewhat off topic, I figured I set the record straight on preference. I am likely in a minority.
 

kwired

Electron manager
Location
NE Nebraska
The millions of them out there used on AC units are mostly 60 amp rated, but a majority of them never see more than 35 amps continuous loading, and a high percentage of those only see maybe 25 -28 amps max. Don't know how well they would hold up to 48 amps continuous loading.
 

jaggedben

Senior Member
I have to tell you as an HVACR guy, I despise those disconnects for several reasons....
1.They are knuckle busters
2.They can cause overloads if you do not stab them perfectly and quickly on a system that has the contactor already engaged
You are correct, they are the CHEAP AC mans favorite, but in real terms just make things more difficult. I consider them the hallmark of a bad install.
While somewhat off topic, I figured I set the record straight on preference. I am likely in a minority.
No that's useful feedback. If I were to switch to these then there had better not be too many problems. That is, for every one that might cause an extra truck roll there had better be 10 or more that don't ever.

I do think that your number 2 issue might not be an issue for solar inverter interconnections, due to the delayed startup.
 

jaggedben

Senior Member
The millions of them out there used on AC units are mostly 60 amp rated, but a majority of them never see more than 35 amps continuous loading, and a high percentage of those only see maybe 25 -28 amps max. Don't know how well they would hold up to 48 amps continuous loading.
Well that's actually true for the vast majority of residential solar inverters as well, not going above 32A. The few that actually go up to 48A we are making a bigger enough profit on those jobs that I can spend 70 bucks on a safety switch.

Useful feedback, but I'm most interested in whether anyone thinks there's a code issue.
 

kwired

Electron manager
Location
NE Nebraska
Well that's actually true for the vast majority of residential solar inverters as well, not going above 32A. The few that actually go up to 48A we are making a bigger enough profit on those jobs that I can spend 70 bucks on a safety switch.

Useful feedback, but I'm most interested in whether anyone thinks there's a code issue.
I think it is dependent on interpretation of what you brought up:

the disconnecting means shall consist of ... switch(es) or circuit breaker(s) with the following [feature]:
...
(2) Externally operable without exposing the operator to live parts...
IMO operator isn't exposed to live parts with such disconnect.

Midwest Electric has a model that has a sliding switch operator instead of a "pull out" if you want to go one step further with non exposure to live parts, and is only slightly higher in price than the pull out version. No pull out to lose either.
 

MAC702

Senior Member
Location
Clark County, NV
Pretty much the same deal for solar inverters, I think, if by 'rarely' you mean that once a unit is installed and commissioned, most are not touched again for a long time. (Or do you mean that most of the time that you yourself operate one, you have the circuit turned off elsewhere?) Also since inverters don't restart immediately when reconnected, it's only disconnecting that one needs to be concerned with load. But these things are load break rated anyway, right?
Pretty much, but as mentioned above, every once in a while you will be putting one in when it's going to start as soon as you do. That can sometimes be a pain, especially on an older one. The new ones seem to work much better for getting it in smartly and fully. I've had to replace a lot more failed breaker-style discos than pull-outs.

One can have a preference but to say using the other is a hallmark for bad install is a stretch. After all, I would never use a backstab on a receptacle! :p
 

MAC702

Senior Member
Location
Clark County, NV
...Midwest Electric has a model that has a sliding switch operator instead of a "pull out" if you want to go one step further with non exposure to live parts, and is only slightly higher in price than the pull out version. No pull out to lose either.
When doing maintenance, I far prefer the pull-outs to the breakers or switch styles. The reason being is I take the pull-out and set it on top of the disco box or machine and can look any time and SEE IT. Sometimes during t-shooting, you will turn power on and off several times. I ALWAYS make sure it's off again when I need it. And I don't leave the lids open to see the breakers or switch because that's a guaranteed way to cut your head open when you hit it.
 
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