Unlimited Voltge Drop

Unlimited Voltge Drop

We normally use the NEC fine print note as a guide for voltage drop which recommends 5% split between the feeder and branch circuit. We also recognize that LEED has a prerequisite 5% max. We're not necessarily aware of another code implied cap on electrical power system design.

A well known design/build power contractor is telling clients that following the 5% guide is costing them 100s of thousands of dollars in upsized feeder costs. They claim to regularly get away with regularly using 7% for voltage drop. When we balked at their VE proposal they said they often also use 80% of the calculated demand load for feeder voltage drop calculations and assume zero percent voltage drop on branch circuit calculations.

We don't see where any smart jurisdiction would buy their arguments, but jurisdictions don't seem to check and developers tend to only see dollar signs. The feeder load is already heavily demanded and no branch circuit has zero voltage drop. None of their assumptions make any sense, but they have their own internal staff of registered engineers and they do tons of their own work around the country.

Are there any qualified opinions out there from registered engineers or code officials that know where the limits are, given that only a fraction of projects are LEED?

Submitted August 10, 2017 at 10:26PM by PennStateInMD
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Unlimited Voltge Drop

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