Would you like to have incoming utility power that was five times more reliable than what you have
How can this be done? Did you know that in some circumstances you could parallel two independent utility
sources, greatly reducing the likelihood that a problem on one source will cause a problem at your facility.
This is because one source can fail and your load continues to receive power without a bump. Other bumpless transfer solutions such as
solid-state transfer switching are far more costly.
However, paralleling multiple sources to a common bus will not be permitted by a utility in many
instances. The most common reason that the utility does not permit the paralleling of two sources
is that the two sources are not sufficiently matched. Unmatched sources cause concerns for the utility including the concern
that power could flow in a reverse direction through one of the sources.
If the problem can be solved by having matched sources, how close must the two sources be to be
considered "matched" and what other parameters could "make or break" the application?
You will need some information to know if you are even a candidate for a spot network installation.
Use this calculator to determine whether your application would be suitable for
a spot network. Use the "Quick Check" calculator below as a first-pass analysis. Use the
Complete Check Calculator to provide a more in depth evaluation on whether your diverse sources
are candidates for a spot network.
Quick Check Calculator
Obtained from your utility bill as "Demand", "Peak Demand", "Billed Demand" or similar. If you don't have
an electric bill enter the "amp" rating found on the main breaker for the facility.
Lower loads means more likelihood of reverse current on one of the networks.
Worst case is zero load. Select the lowest normal load you expect.
Starting at the main breaker or fusible switch, trace the circuit towards the utility until you reach
the first transformer. If this transformer is owned by the utility, a call to the utility will usually
result in your obtaining the information. If unsuccessful, select the "Not Sure" and the program will
estimate the transformer rating as five times your incoming needs (assumes other customers are also using
this transformer). Estimating that the upstream transformer is oversized is a conservative estimate
since the likelihood of two mismatched sources successfully supplying a spot network decreases as the
upstream transformer increases (actually as the upstream impedance decreases, but that is saying the
"%Z" is percent impedance. Provided on nameplate of transformer.
This is the rating of the proposed second source for your facility. As with question 4, you can obtain
this information from your utility. If unsuccessful, select "Same as above" and the program will
assume that the values for Source 2 are the same as for Source 1. For best operation, it is beneficial
to have both source transformers having the same kVA and impedance ratings.