downsizing main breakers [RE-wrenches]

[Steve Johnson]

The easy way to measure the load is put an amprobe around the incoming 
service conductors at the panel and turn on everything in the house that 
can be turned on, and I mean everything!  Then check the other leg.  
Neutral should be the difference between the two.  If you are 120 amps 
or less (80% of 150) you are good to go.  You could go above that, 130 
or 140 amps with the owners agreement, since a second source of power is 
being added. Loads can be added to any panel anywhere thereby 
overloading any service, ie, you can overload that 200 amp breaker too - 
some future owner could.  But I would definitely find out if they have 
natural gas or propane and what it runs.  The point is to design for 
current known and expected conditions.  Besides, by downsizing the main 
overcurrent protection you are providing more protection not less.  The 
point is not to downsize beyond potential existing or known planned 
future loading.

Secondly taping the service overhead is not as hard as it may seem.  The 
tap someone mentioned earlier is called a Kupltap.  It is insulated and 
can be applied hot if you have experience doing such a thing.  It has 
teeth that sink into the insulation and tap the main conductor.  It 
tightens down with a socket wrench and the bolt that squeezes it is 
insulated from the wiring so there is no exposure to hot wires during 
the installation.  Of course you would turn off the house main and 
inverter disconnect during installation so no current is flowing.  The 
advantage here is not needing the utility to shut down the transformer 
secondary, not having to wait for the service release inspection 
(depending on relation to local AHJ) and not having to strip the main 
conductors. Just run a 3/4" or 1" service riser with #6, put a 
weatherhead on it, and go to a 3R 60 amp fused disconnect. See 
240.21(B)(5)Outside Taps.



geoff at third-sun.com wrote:
> 
> Wrenchtastic list members, What steps do you take (and what part of the 
> NEC
> is referenced) when deciding to downsize a main breaker for busbar 
> loading
> issues?  My client is ready to "wing it" and slap a 150 amp breaker into 
> the
> 200 amp panel, and this is an un-inspected job, but what about nuisance
> trips? sizing a service seams very elementary, but I would like to know 
> the
> proper way to do it!
> 
> Happy weekend to all and safe travels to the folks returning from San 
> Jose
> 


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