Homeowner Forum / Construction / December 2005

Constant Voltage Transformer  (CTV)

Another poster mentioned a constant voltage transformer.  One of these
large enough to protect a whole house would be very, very expensive,
even for only 100 amp service.  To protect against voltage spikes, there
are surge protectors that are relatively cheap and can be installed at
the breaker panel.  A standby generator can be used to protect against
really low voltage.  There are also voltage monitors that can trigger a
contactor or relay in response to high or low voltage.  The ICM491
(icmcontrols.com) is an example.  These are usually used to protect
sensitive equipment like AC or refrigeration equipment.  They could be
used for a whole house in conjuction with contactors capable of handling
the current load.  These are on/off devices; they disconnect the
equipment when the voltage is out of range.  Most items in a house
though can handle a pretty wide swing in voltage.  In makes more sense
to protect sensitive items like electronics, AC, refrigerator, well
pump, sump pump, etc. rather than the whole house.

For point of use:  A UPS (uninteruptable power supply) for a computer will
do this.  During an undervoltage event, how much load each one can handle
and for how long depends on its battery size.  Overvoltagbe events are
handled by a MOV.

A whole house MOV will protect from overvoltage, combined with a generator,
this would be the most conventional solution for black and brown outs.

Or are you looking ofr a device that wioll kill all the power if the voltage
falls to low.  I'm not shure what that is but it would be a lot less
complicated than something that tries to maintain power levels.

Thanks to all who have replied.  It's a rather long story, but my son
had a Guardian standby-generator installed, something like this one:

http://www.guardiangenerators.com/products/guardian7_15kw.asp

On it's first use, after about 30 minutes' operation, certain
appliances in the house started to smoke, and ultimately had to be
replaced at great inconvenience, to put it mildly.

A present theory seems to be that the generator's voltage output
regulator system failed, and sent too much power into the house wiring.

I'm no electrical expert by any stretch of the imagination,and it may
seem redundant, by I was thinking maybe he could get one of these
external "contant voltage transformers" to install between the
generator output and the house wiring as back-up protection against
over/under voltages coming from the generator.  With all the misery
that he had to go through with this failure in New England cold
weather, just might justify the extra protection.

I would appreciate any further comments!

Thanks again for the helpful replies.  The problem is at my son's large
house in rural New England, and I'm in Texas.

He told me that several appliances were damaged, including an electric
wall oven (not a micro wave).  He said the oven was not turned on at
the time of the incident.  I forget for the moment what all blew, but
it included TVs, etc.  I asked him if he had surge protectors in his
computers and he said yes, and that one smoked the computer and the
other one didn't, perhaps indicating differences in the two surge
protectors on those computers.

Let's assume for the moment that capacity is sufficient, because we
went over the total wattages involved,

I/we, of course, didn't know about Honda generators having better
protection.  My son says he just went to the local Home Depot, they had
these Guardians generators and convinced him this is one would do the
job - and referred him to a guy that is supposed to have the exclusive
contract for installing Guardian generators in that part of the
country.

I told him to get actual measurements of the output voltage from the
generator when his Guardian electrician/installer comes back.  My son
didn't know what the guy was talking about when he came out to see what
happened, but the guy told him the lines measured something like 130 on
one side and 157 on the other.

I agree the solution belongs to the generator, which is now supposedly
repaired.  BUT, he is afraid to give it another chance, given the grief
that it gave him with this experience - hours without power in 15 deg.
temperature, and then more hours/days to get his appliances repaired.
That's where I came up with the possibility of the second (redundant)
protection.

Another local friend of mine told me to tell my son to have the
electrician check out the neutral/ground conductor in the cable to make
absolutely positive that is is connected properly and tightly.

I agree that Guardian should make available the claimed voltage limits
for over-voltage protection, and that it must not output destructive
high voltages.  I'll tell him to contact Guardian and get the
over-voltage protection specs.

P.S.: Would some one please tell me what they mean by "MOVs" ?

As an aside, he has bears coming up and looking into his windows and
scaring them heck out of him and his family!