Page 50 - Boiler Operator’s Handbook

Operating Wisely 35

Just the same, you should be able to do it. Read the minal 4 in the panel. To quickly isolate a problem start
drawings and sequence of operation until you under- testing at the middle of the circuit, and terminal 4 is in
stand how your system works then review it every year the middle in this example. If the light works then the
so you will have most of it in your head when the need break or open is closer to the grounded conductor and
to solve a problem comes up. you can forget checking everything before terminal four.
What good was that test lead? Well, all you had If the light doesn’t work then the break or open has to
to do was touch the end of it to one of the terminals or be between the hot lead and terminal four. Once you’ve
wires in the system (while holding the insulation on the figured out which side contains the open you can test at
wire so you don’t light up) and see if the test light comes a point near the middle of the part of the circuit that you
on. If the light comes on then there’s a closed circuit just isolated. You should pick terminal 3 or 5 depending
up to that point. If it’s not on then you know there’s an on which end of the circuit must have the break because
open somewhere between the power supply and that they’re conveniently in the panel. If the light didn’t
terminal. When one terminal is hot and the next one isn’t work at 4 or 3 then check the wire connected at the on/
you can look on the drawing to see what’s connected off switch because it’s also conveniently in the panel.
between the two. If it’s supposed to have a closed con- You’ve isolated a problem when you find the spot where
tact at the stage you’re looking at then you go out into the light doesn’t work when checking after a device and
the plant to find the device to see what’s wrong with does before it. Of course that doesn’t mean that there
it. The device could be broken or it could be valved off isn’t a problem with something else in the circuit that’s
(although there aren’t supposed to be valves between between the problem you found and the left connection
a boiler or burner and the limit switches). It could be of the FMS. It’s slightly more complicated because other
something as dumb as a screw vibrated out and the parts of a circuit must be activated first but once you
switch flopped over, something that really screws up determine where the circuit is open it’s a lead to finding
mercury switches. out what’s preventing operation.
Figure 1-10 is an example of a circuit test. For some If a fuel safety shut-off valve should open, but
reason the fan motor starter (FMS) coil isn’t energiz- doesn’t, you can check its terminal (when the burner
ing to start the fan. The test light is connected to the management system indicates it should be energized)
grounded conductor. That upside down Christmas tree to see if it’s getting power (light on). If it isn’t then you
symbol is normally used to represent a ground wire can check back through the panel circuitry to find what’s
connection. The clip on my test light allows me to slip open. Keep in mind that you only have ten or fifteen
it over any grounded metal part of the boiler plant for seconds to do that most of the time and you’ll have to go
testing but there’s times when something accessible through several burner cycles until you spot the prob-
and metal isn’t grounded even if it should be so don’t lem. If the output terminal is energized then you’ll have
count on it. The other side of the light is connected to a to check the power at the valve to be certain it’s not a
test lead with an insulated handle and extended metal loose or broken wire between panel and valve motor.
probe. Mine was recovered from a broken meter that I used to take it for granted but got stung so many
someone threw away. Always check your test light by times that now I always check to be certain a burner
tapping a hot lead to ensure it’s working before testing. management system is properly grounded. Lack of
You’ll note the test lead is indicated to be touching ter- a ground can produce some very unusual and weird
conditions. Anytime you see lights that are about half
bright or equipment running that’s noisy and
just not normal look for lack of a ground or an
additional one.
Exactly what is a ground? It’s anything
that is connected to a closed circuit to mother
earth. In most plants there is a ground grid, an
arrangement of wires laid out in a grid under-
ground and all interconnected to each other and
the steel of the building to produce a ground-
ed circuit. At your house it’s your water line
and possibly also separate copper rods driven
Figure 1-10. Testing a control circuit straight into the ground. A ground wire is any