Line side taps

Status
Not open for further replies.
sketchy

sketchy

Senior Member
Location
MN
If I have a 200 amp service and I do a line side tap in the meter with milbank k4977 tap lugs, does that mean I can only feed a system up to 40 amps based on the 120% rule? Or is it the meter socket rating I need to be concerned with? I have been tapping the meter with as much as 80 amps and having them pass inspections. But if I look at 705.12(A), is it the service rating of the breaker rating?
 
sketchy said:
But if I look at 705.12(A), is it the service rating of the breaker rating?
Click to expand...

It's the service rating. 705.12(A) is very explicit about that, at least if you're looking at the 2011 code.

The service rating is whatever the 'weakest link' is on the utility side of the service disconnecting means, among service conductors, meter socket, etc. You can usually assume that it is the same as the rating of the service disconnecting means. It shouldn't be less, it might be greater.
 
sketchy said:
If I have a 200 amp service and I do a line side tap in the meter with milbank k4977 tap lugs, does that mean I can only feed a system up to 40 amps based on the 120% rule? Or is it the meter socket rating I need to be concerned with? I have been tapping the meter with as much as 80 amps and having them pass inspections. But if I look at 705.12(A), is it the service rating of the breaker rating?
Click to expand...
Since this is a line(supply)-side tap connection, the 120% rule does not apply at all, and you could theoretically backfeed up to the entire service rating. That is why you "got away with" 80A on a 200A service. :)

One oddball note: If you were to backfeed the entire service rating and you also put only extremely low PF loads on the service, you could actually overload the weakest link in the service, since the vector sum of the currents could be larger than the backfeed alone. But the Code does not seem to care about that case. (And no, I am not going to generate a proposal. Let sleeping dogs lie. YDMV.)
 
Last edited:
So if I have a 600 amp service in an apartment complex that has a 200 amp house panel on it's own 200 amp meter socket, could I add 150 amps of solar to the load side of the meter without issue? That's how I understand it.
 
sketchy said:
So if I have a 600 amp service in an apartment complex that has a 200 amp house panel on it's own 200 amp meter socket, could I add 150 amps of solar to the load side of the meter without issue? That's how I understand it.
Click to expand...
That is how I understand it too.
But I would not be willing to risk a lot on my belief that it does not matter how many other meters, of what sizes, are also connected to the 600A service.
 
There may be issues for 150A inverter output. As I understand it 'sketchy' has:

600A main service

possible 600A meter

Distribution buss

200A meter for apartment

200A OCPD

connection for panel


This is likely a meter stack (modular metering), and if such it is not listed for any internal connections.
The possible issues are:
-- The ratings of the distribution buss to the 200A meter and 200 OCPD and the 120% rule[690.64/705.12(D)(2)];
-- Rating of the connection for the distribution panel an application of the 120% rule to that.

Only obvious place to connect is the 200A OCPD. Required ampacity of the connection is (200+150)/120% = 291.7A. Depending on other factors, that is 300mcm or larger that the OCPD must accept. If you have smaller wire, sized only for 200A, you have to replace it.

Then check the ampacity of the line side buss going to the 200A meter. If not sized for 291.7A, you have an issue. Internal buss is seldom specified and may have to be calculated or consult the factory. The question becomes 'At what point does the 200A service start?'.

I had this issue to deal with for 120A inverter connected to 200A OCPD (serving loads) on a no main device service entrance and had to apply the 120% rule to all cables from the 200A SES OCPD to the AC combiner panel. AHJ did not question the internal buss rating.
 
sketchy said:
So if I have a 600 amp service in an apartment complex that has a 200 amp house panel on it's own 200 amp meter socket, could I add 150 amps of solar to the load side of the meter without issue? That's how I understand it.
Click to expand...
Is there a 600 amp service disconnect that feeds the meters?
 
It is a 600 amp main disco that feeds a bank of 12 meters (I think, going by memory) each with a 100 amp breaker. The individual meters are fed by lugs attached to the buss bar. At the end opposite the disco, a set of 3/0 copper taps on to the buss, goes through a 200 amp meter socket, then into a 200 amp panel. This is the house panel that I need to feed the solar to. One thought was to change the meter to 320 amp with dual lugs. Another thought was polaris lugs in the panel. Thoughts?
 
705.12(A) refers to the service disconnecting means, so if the 600A disco is the service disconnecting means, then this isn't a supply side connection (aka line side tap). Thus the 120% rule comes into play. To backfeed 150A you need a busbar rated 625A. Or else, if the busbar is rated 600A, maybe you can downsize the existing fuses to 500A. Otherwise your limited to 120A.

Possibly the 600A disco is not considered to be on the load side of the service point and is thus not the service disconnecting means. The utility could tell you that. In that case either of the methods mentioned in your last post would be okay IMO (and I don't see why you need the meter socket to be rated more than 200A).
 
Status
Not open for further replies.
Top