Critical loads panel with 2 power sources, interlocked. Do I have the neutrals wrong?
- Thread starter Rokkerhead
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timselectric
If I can do it, you can do it.
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That's the easiest and cheapest way to do it.use something like this in the subpanel?
And what I prefer.
Or like this on a Square D QO panel (panel is on inverter load as shown):
One thing to be VERY careful about is that the interlock is on the panel COVER. If you take the cover off, as many of us are wont to do, you lose the interlock and can now do very bad things to your system like tie inverter output to grid directly. BE REALLY CAREFUL when manipulating these breakers with no cover on.
Something I recommend on all these types of interlocks is to carefully watch the phasing of L1 and L2. A hybrid inverter operating grid tied will basically pass GRID input to LOAD output directly through relays such that grid L1 is load L1. If you invert the phasing at the interlock, an accidental activation of both breakers will result in L1 tied to L2. You can guess what happens next.
If, instead, your interlocks are phased correctly, so that if you accidentally turn both on, L1 goes to L1, the badness of that is much reduced over an L1 to L2 short. It isn't good, but it isn't nearly as catastrophic.
You need to be careful with some main breakers, they swap L1 and L2 sides as they pass through the breakers. The QOM main breaker (like the 60 amp one above) does this. The left lug actually comes out the right breaker terminal and vice versa.
The best way to check phasing is to run the panel on the grid only with inverter breaker off and use a volt meter from inverter L1 on the breaker terminal to bus bar L1 and see that you get little to no voltage. Check L2 to L2 also. Then you have the phasing correct. If you get 240 VAC, then you phasing is backwards and you should reverse one connection, either the main breaker or the inverter load breaker.
The phasing thing is just one little safety in case something bad happens.
Mike C.
One thing to be VERY careful about is that the interlock is on the panel COVER. If you take the cover off, as many of us are wont to do, you lose the interlock and can now do very bad things to your system like tie inverter output to grid directly. BE REALLY CAREFUL when manipulating these breakers with no cover on.
Something I recommend on all these types of interlocks is to carefully watch the phasing of L1 and L2. A hybrid inverter operating grid tied will basically pass GRID input to LOAD output directly through relays such that grid L1 is load L1. If you invert the phasing at the interlock, an accidental activation of both breakers will result in L1 tied to L2. You can guess what happens next.
If, instead, your interlocks are phased correctly, so that if you accidentally turn both on, L1 goes to L1, the badness of that is much reduced over an L1 to L2 short. It isn't good, but it isn't nearly as catastrophic.
You need to be careful with some main breakers, they swap L1 and L2 sides as they pass through the breakers. The QOM main breaker (like the 60 amp one above) does this. The left lug actually comes out the right breaker terminal and vice versa.
The best way to check phasing is to run the panel on the grid only with inverter breaker off and use a volt meter from inverter L1 on the breaker terminal to bus bar L1 and see that you get little to no voltage. Check L2 to L2 also. Then you have the phasing correct. If you get 240 VAC, then you phasing is backwards and you should reverse one connection, either the main breaker or the inverter load breaker.
The phasing thing is just one little safety in case something bad happens.
Mike C.
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