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Previously, we said that if your motor supply doesn't conform
to Art. 430, you'll have a "high maintenance" situation. Conformance
with Art. 430, however, doesn't necessarily produce a "low maintenance"
situation. Not even in an NEC sense.
For example, consider voltage drop, per the informational note in
210.19(A). You calculate this during the design. If you try to measure
it in an installed system, you actually measure a combination of voltage
drop and losses (through insulation and across connections) in the run.
This measurement can reveal that something is wrong. If you measure 430V
at the supply terminals to a 480V motor, you don't need to calculate
voltage drop to know you have a problem. But what exactly is the
problem?
To answer that question, calculate the voltage drop between the
motor and its supply. Then, compare that to the measured voltage loss.
If the two numbers are close, you have a design problem — undersized
conductors. As the numbers grow further apart, your problem is
increasingly a maintenance one.
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Your plant has been using the same electrical testing firm
for many years. One task that the firm handles for you is cable testing.
They've always been good at getting in and out, never causing a shutdown
to run past schedule — and that includes replacing cables as needed.
This year, however, their project manager told you there were too many
cables to replace within the allotted time. He suggested scheduling
another shutdown just for that purpose as soon as planning and staffing
could permit.
What do you tell your boss?
Visit EC&M's website
to see the answer.
Suppose you're taking neutral-to-ground (N-G) voltage
measurements at a convenience receptacle in the cabinet where circuit
boards were turning to toast. How do you know when these measurements
indicate there's something wrong?
If you see a volt or two, you have no worries (much higher than
that is a bad sign). But if you see 0.10V or less, you may have found
the smoking gun. Why?
To read more on this story, visit EC&M's website.
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Commonly misunderstood/misapplied terms, part
5. - Grounded conductor. In many wiring systems, the
neutral conductor is intentionally connected to ground (earth). But not
all systems are grounded, so you can have a neutral that isn't a
grounded conductor. Take care you don't blithely use "grounded
conductor" and "neutral" as synonyms or, in the field, treat them as
such.
- GFCI/AFCI. At one time, if you wanted a current trip
device your only choice was a fuse. In many applications, a fuse is
still an excellent choice. But, like a circuit breaker, it's an
overcurrent device designed to protect wiring. It's not a current trip
device to protect people. Although there are combo GFCI/AFCI devices on
the market, only the GFCI function protects people from shock. An AFCI
isn't a "better GFCI," it's a different device for a different purpose.
- Identified. The particular device or electrical
equipment is suitable for the intended use. Try to buy a "ground rod,"
and your electrical distributor/supplier won't sell you 10ft of schedule
80 pipe. The rod you get will be identified for that use via listing
and/or labeling by a qualified product evaluation
organization.
If you've worked with many solvents or other chemicals on the
job, you've seen a Material Safety Data Sheet (MSDS). If you haven't
seen an MSDS for each chemical, there's a deficiency in your company's
safety program. Seeing and understanding aren't the same thing, though.
Unfortunately, an MSDS can have an "eyes-glaze-over" effect if you don't
know how to use it to get the information you need.
So, let's get a grip on what that MSDS actually is. The first
thing to understand is it's a structured report. That structure consists
of seven sections, each with a specific purpose. For many chemicals you
might use, one or more of those sections will contain "N/A" instead of
having information. This doesn't mean the MSDS is incomplete. It means
that section doesn't apply to the chemical you're using.
In our next issue, we'll start looking at the sections of an
MSDS.
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