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Testing an Electric Blanket

N

Nelson

Jan 1, 1970
0
Bob,
You might try a heating mattress pad instead.

I was unaware that they existed until you pointed it out. Most seem to
operate on low voltage DC which is, of course, inherently safer. And I
notice that there are even some blankets that do also. I think I will
definitely try one if the "space blanket" solution doesn't pan out.
If you cannot afford one, send me a response & I'll have one shipped
to you free of charge.

I think I can swing one if necessary, but I appreciate your generous
offer. I am frequently amazed at the kindness of strangers on usenet.
 
I

ian field

Jan 1, 1970
0
Bill Jeffrey said:
I'm not sure a GFI would do any good. All electric blankets I have ever
seen are two-wire devices, and there is no ground in or around the
blanket. No ground = no ground fault = happy GFI.

I did see a blanket fail once, out in the middle of the blanket (i.e., not
near the connector). I THINK the failure mechanism was a heating wire
that had been flexed enough that it was ready to break - but hadn't quite
broken yet. The fracturing wire got thinner, which increased the
resistance at that point, which overheated the wire at the incipient
break, which caused a hot spot that was hot enough to scorch the blanket
material (the material does not support flame, by the way).

This was NOT a short circuit. The heating wires are well separated, and
anchored in place quite well.

Bill

Ground fault current interrupters do not sense ground current directly -
they sense any difference between the current in the line and return wires,
if the line current exceeds the return current then it must be going
somewhere it shouldn't!!!
 
I

ian field

Jan 1, 1970
0
mc said:
Right, but still not much of a help with an electric blanket, since there
is unlikely to be another path to ground. The hazards are: (1) a fire, or
(2) person in bed making electrical contact with the heating element at 2
points that are at substantially different voltages.

If there's no other path to ground - getting electrocuted might be
difficult!
 
B

Bob

Jan 1, 1970
0
Nelson,
Although I don't like Terrel's attitude, he had one of the best answers
about measuring the AC current. Gives an incomplete assessment, but a
good indicator. The other thought is to use a "voltage sniffer" if you
have one, to check various areas of the blanket to see if they are
working (getting voltage/current). My daughter always liked the effect
of the heating mattress pad. Because heat rises, it was more "toasty"
for her.
Bob
 
J

jakdedert

Jan 1, 1970
0
James said:
Maybe they're just not built like they used to be. My grandma has one
that's at least 40 years old, it's on the bed in a spare room now and
when I've stayed there I still never turn it up past 3 or so, set it to
5 or 6 and I'm sweating, it goes all the way up to 10.
That's nothing...I used to have one that went all the way up to *11*!
<G>

jak
 
T

T Shadow

Jan 1, 1970
0
jakdedert said:
That's nothing...I used to have one that went all the way up to *11*!
<G>

jak
So you don't really know how much the blanket was actually used. Ours are in
daily seasonal use. My wife never uses less than 5 even on new blankets so
that must shorten the life considerably. Not unusual to wake up sweating
just from the heat from her side.

Present blanket goes all the way to Hi. :^b
 
B

Bill Jeffrey

Jan 1, 1970
0
ian said:
Ground fault current interrupters do not sense ground current directly -
they sense any difference between the current in the line and return wires,
if the line current exceeds the return current then it must be going
somewhere it shouldn't!!!
Ian -

You are right - thanks for the lecture.

I phrased my objection badly, but I was responding to a previous post
that suggested a GFI could protect against line-to-line shorts, or
shorts across part of the heating element. I stand by my statement that
if there is no ground anywhere, there cannot be a ground fault. So the
question becomes, as another poster noted, where will you find a ground
connection if you are snug in your bed, and if the power cord (a
two-wire cord) doesn't bring a ground into the picture? I suppose that
if you set up your bed in a bathtub, you might do it. But as I look
back, I have never had a ground connection within casual reach of any
bed I have ever slept in.

OK, so now all of you lecturers can tell me about beds set up against
steam radiators, copper water pipes run along the wall, radio antennas
tacked to the wall, antique light switches, etc. I'm not sure that does
the OP any good. On the other hand, if he uses and trusts a GFI, based
on your comments, he could be in big trouble in case of a real short.

Bill
 
M

Michael A. Terrell

Jan 1, 1970
0
Bill said:
Ian -

You are right - thanks for the lecture.

I phrased my objection badly, but I was responding to a previous post
that suggested a GFI could protect against line-to-line shorts, or
shorts across part of the heating element. I stand by my statement that
if there is no ground anywhere, there cannot be a ground fault. So the
question becomes, as another poster noted, where will you find a ground
connection if you are snug in your bed, and if the power cord (a
two-wire cord) doesn't bring a ground into the picture? I suppose that
if you set up your bed in a bathtub, you might do it. But as I look
back, I have never had a ground connection within casual reach of any
bed I have ever slept in.

OK, so now all of you lecturers can tell me about beds set up against
steam radiators, copper water pipes run along the wall, radio antennas
tacked to the wall, antique light switches, etc. I'm not sure that does
the OP any good. On the other hand, if he uses and trusts a GFI, based
on your comments, he could be in big trouble in case of a real short.

Bill


In that case you need the new arc detect circuit breaker that kills
power when something sparks. The US electrical code requires them for
new construction because a lot of electrical fires start in bedrooms due
to damaged cords and appliances. I am in the process of making a new
control cable for my hospital bed. If it was the power cord that was
damaged, I could have had a nasty fire.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
P

Paul Hovnanian P.E.

Jan 1, 1970
0
GregS said:
The test would only trip the integral ground fault interupter
if there was leakage. I have a feeling most all blankets now come with
fault interupters. Is that true??

I think I've seen blankets with them. I know I've seen hair dryers with
them. If the OP suspects his current (no pun intended) blanket as having
a defect, perhaps it would be better to discard it and obtain one with
the latest safety features.
 
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