[RE-wrenches] Three Inverters, One Disconnect?

[Bill Brooks]

Don and Garrison,

 

The word “dedicated” means “no loads”. That is why, the way the code is written today, you cannot plug a microinverter into a wall outlet. There is no limit to the number of inverters that can be placed on a single breaker. The limitation for inverters, is the maximum overcurrent device specification for the inverter and the ampacity of the conductors being protected by the inverter output circuit breaker in the ac panel.

 

There are emphatically single pole breakers for 277Vac single phase circuits and it is completely valid to place 277Vac single phase inverters on these breakers. There is no need to place them on 3-pole breakers, nor does it provide any significant benefit to turn off inverters on other phases when one phase faults or goes down. Sometimes utilities get crazy on this point and require single phase inverters to have this capability. There are several single phase inverters on the market today with RJ45 jacks in order to trip the other two inverters on different phases when one inverter trips. This comes from utility requirements and is absolutely ridiculous. This all proceeds from 705.100 in the 2011 NEC and prior that was very poorly worded. The wording was updated and improved in the 2014 NEC to make it clear that single phase inverters on 3-phase services is just fine and that imbalances are handled the exact same way imbalances are handled with single phase loads on 3-phase services.

 

Until utility commission ban single phase loads on 3-phase services (that’s a joke—it will never happen), we should always be allowed to put single phase inverters on 3-phase services. As we do this smartly and correctly, we reduce site voltage imbalance rather than increasing imbalance.

 

Bill.

 

 

 

 

 

From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of don at energysolarnow.com
Sent: Friday, April 04, 2014 11:36 AM
To: re-wrenches at lists.re-wrenches.org; Garrison Riegel
Subject: Re: [RE-wrenches] Three Inverters, One Disconnect?

 

Hi Garrison- The dedicated breaker referred to in 705.12(D)(1) means they do not want the inverters plugged into branch breakers. One (and only one) inverter into each pole of a 3-pole breaker seems safer and better than 3 individual breakers, and seems to fit the definition of "dedicated" breaker.

I don't know that you can even find single-pole 277 Vac breakers....

DonB

-------- Original Message --------

Message: 6
Date: Fri, 4 Apr 2014 08:01:00 -0500
From: "Garrison Riegel" <garrison at solarserviceinc.com <mailto:garrison at solarserviceinc.com> >
To: <re-wrenches at lists.re-wrenches.org <mailto:re-wrenches at lists.re-wrenches.org> >
Subject: Re: [RE-wrenches] Three Inverters, One Disconnect?
Message-ID: <828201cf5005$edd065b0$c9713110$@solarserviceinc.com <http://solarserviceinc.com> >
Content-Type: text/plain; charset="utf-8"

Hi Don,

Thank you for your reply. Good idea on the single 480V inverter, but multiple subarrays at different tilts/orientations and strings lengths make that impractical unfortunately. 

It also seems like a good idea to use a single 3-pole breaker to prevent phase imbalance, but I thought each inverter required a dedicated breaker as per 705.12(D)(1). Thoughts?

Thanks,

Garrison

From: don at energysolarnow.com <mailto:don at energysolarnow.com>  [mailto:don at energysolarnow.com] 
Sent: Thursday, April 03, 2014 1:55 PM
To: re-wrenches at lists.re-wrenches.org <mailto:re-wrenches at lists.re-wrenches.org> ; Garrison Riegel
Subject: RE: [RE-wrenches] Three Inverters, One Disconnect?

With single phase 240 each inverter output is two poles; but since you are using 277 each inverter output is between one pole and neutral, so you could indeed use a 3-pole disconnect since the neutrals are not switched.

A 3-pole breaker is usually used with 3-phase systems, but since there are 3 separate inverters it is legal to use 3 single pole breakers provided you get them into separate phase poles. However, there would be a phase imbalance if one breaker tripped and the others were still sourcing current, so it's better to use a 3-pole breaker here. 

But rather than go to all the work of wiring 3 separate 3.6 kW inverters, why not just use the PowerOne 10.0 or 12.0 kW 3-phase inverters? This would be less expensive and would need just one conduit run for input and output.

Don Barch

Energy Solar





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