Safe to Perform a Line Side Tap?

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Matu

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Solar Field Engineer
I have a 100amp Cutler Hammer MLO box supplying a house. Using a 7600H-US SolarEdge Inverter, using a fused disconnect with 40A fuses in it as OCPD. The main disconnect switch for the house is likely at the meter, but not sure. One of those switches are feeding an Air-Conditioner dedicated subpanel with fuses in it. Is it safe to perform a line side tap on this panel?

And as a general note, is it safe to perform a line side tap on a MLO?

EDIT:
Due to a lack of photos (I'm designing based on site visits our construction crew took), I'm not really sure if that Air-conditioner fused disconnect is feeding the MLO or being fed by the MLO. In this case, is it still safe to tap?

MLO1.PNGMLO2.PNG
 
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If you use an approved tap device and you have no load on the tap, then it should be safe. I have done them and seen many others done. If you can turn off the power to the conductors being tapped, it's even safer.
 
Not exactly sure of inspections or not, but will it matter that it’s only a three wire and not a four wire?
Looks like about a dozen grounds under the same lug also..
 
Coppersmith said:
If you use an approved tap device and you have no load on the tap, then it should be safe. I have done them and seen many others done. If you can turn off the power to the conductors being tapped, it's even safer.
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Would it still be considered safe if that fused disconnect were acting as the OCPD for the MLO? Or if anything with old fuses acting as OCPD? I've read somewhere that installing solar (or anything new for that matter) should be avoided if fuses are involved.
 
Coppersmith said:
If you use an approved tap device and you have no load on the tap, then it should be safe. I have done them and seen many others done. If you can turn off the power to the conductors being tapped, it's even safer.
Click to expand...
I meant if it was safe within NEC code.
 
The pictures do not seem to show a service disconnect, at least not a code compliant one.

If the conductors landing on the lugs of the MLO are a feeder, then it is a load side tap, and you have rules that come into play about overcurrent protection. See article 705. I don't think you're going to be able to do on that CH panel, given the combination of rules and practical considerations there.

You can't just make assumptions about upstream disconnects or panels when considering solar backfeed. If your crew failed to get the pictures of the meter and how if feeds the stuff we see then someone will have to go back and get them.

Finally, unless you are trying to backfeed that fuse box with solar, or unless you somehow tap its feeder without properly protecting it, then its safety isn't whatsoever affected by having solar on the premises.
 
jaggedben said:
The pictures do not seem to show a service disconnect, at least not a code compliant one.

If the conductors landing on the lugs of the MLO are a feeder, then it is a load side tap, and you have rules that come into play about overcurrent protection. See article 705. I don't think you're going to be able to do on that CH panel, given the combination of rules and practical considerations there.

...
Finally, unless you are trying to backfeed that fuse box with solar, or unless you somehow tap its feeder without properly protecting it, then its safety isn't whatsoever affected by having solar on the premises.
Click to expand...

So if that fused AC disconnect were the service disconnect in our case and we decided to tap between it and the meter, why would it not be code compliant (and would it be technically safe given your response)?

jaggedben said:
You can't just make assumptions about upstream disconnects or panels when considering solar backfeed. If your crew failed to get the pictures of the meter and how if feeds the stuff we see then someone will have to go back and get them.
Click to expand...
I agree. Just looking for potential solutions to the potential scenarios for now.

Also, if this were an MLO panel with the '6 service disconnect'/split busbar configuration where one of those main breakers feeds the rest of the busbar below it, would a line side tap (tapping the feeder conductors feeding the entire panel) be code compliant there too?
Our AHJ has passed line side taps on MLOs with that configuration before (protected with an installed fused AC disconnect), some even where there are already 6 service disconnects installed.

Or what if the meters had service switches within them, would those be considered service disconnects forcing us to tap at the meter?
After some time of research, it seems like everyones' AHJs does things/interprets code and equipment very differently and it reallllly complicates supply side taps for me.
 
To repeat, a true supply-side connection is only done ahead of the service disconnect, and is a completely separate rule. It's 705.11 in the 2020 NEC or 705.12(A) in previous codes.

If the tap is load side of the service disconnecting means, there's a whole other set of rules to follow, in 705.12 or 705.12(B) or (D) depending on whoch code you're on. Being compliant with these rules depends on the feeder size and the upstream overcurrent device and other things, so its not possible to give a simple yes or no as to whether a tap may be compliant without having more complete information.
 
Wanted to update everyone on this. After going back to the site, we were able to determine that the fused disconnect was actually the service disconnect for the house. We've performed a line side tap on it, now waiting on inspection for results.
Thanks to everyone who has contributed to this thread.
 
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