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Electric dryer - thermal fuse question

M

Michael Kennedy

Jan 1, 1970
0
Thanks Sam

The AC cord (3 wire setup) and wiring block for continuity? Yes.

The 240v socket? No. How do you check it properly? 0-115 on both sides? Or
115 to 115 for 240 volts? All of the "how to" books avoid the testing
procedure for 240v outlets and I don't want to do it until I know how to
do it.

It is easy. Check it both ways. It should show 120v from hot to neutral on
one side and 120 from hot to neutral on the other side. This will let you
know that your hot and neutral is working. You can also measure hot to hot
and you should have 240v. A 240v circuit is really 2 120 circuits in 2
different phases so there is potential between them. Not sure if phase is
the correct term here, but gets the same idea.
FWIW it's a dual circuit breaker on the panel. It didn't trip when the
dryer went dead.

The breaker can be tripped and appear to be closed. You should open and
close breakers to be sure.

Mike
 
W

William Sommerwerck

Jan 1, 1970
0
I'll venture that what you are looking at is not a real thermal fuse,
a device with a metal link that melts (fuses) when it fails. Those
will not recover at all after failure.

How could such a device provide protection? You don't want a fuse "fusing"
to a short!

More likely what you have is a thermostatic switch that opens a circuit
by the motion of a bimetal strip. These will recover when cool. Replace
it and you should be done.

Unless the thermostat is broken, how will this fix the problem? If the dryer
has such a thermostat, and it opened, it most likely opened BECAUSE THERE
WAS AN EXCESSIVE LOAD elsewhere in the circuit. And the OP has to find that,
and fix it.
 
C

Charlie Bress

Jan 1, 1970
0
William Sommerwerck said:
How could such a device provide protection? You don't want a fuse "fusing"
to a short!



Unless the thermostat is broken, how will this fix the problem? If the
dryer
has such a thermostat, and it opened, it most likely opened BECAUSE THERE
WAS AN EXCESSIVE LOAD elsewhere in the circuit. And the OP has to find
that,
and fix it.
If it is what I am thinking about it is not a fuse at all. It is a
thermostat inline with the motor and senses temperature to shut down if
there is an over temp condition. Dryers have several in various locations.
If the OP has one that is defective it may open prematurely. Take it out to
test it and it cools off and resets.

Of course, I could be all wet. I can't see the wiring diagram and have no
model info. It is unlikely that a real fuse would recover. Part of the
fuse rating indicates the highest voltage a fuse is supposed to successfully
open.


Charlie
 
R

Rick

Jan 1, 1970
0
Michael said:
It is easy. Check it both ways. It should show 120v from hot to neutral on
one side and 120 from hot to neutral on the other side. This will let you
know that your hot and neutral is working. You can also measure hot to hot
and you should have 240v. A 240v circuit is really 2 120 circuits in 2
different phases so there is potential between them. Not sure if phase is
the correct term here, but gets the same idea.




The breaker can be tripped and appear to be closed. You should open and
close breakers to be sure.

Mike

Hi Mike

Opened and closed the breaker several times, of course. But what does
this mean?:

Set the meter to AC 750v range. Closed the breaker. Tested black to
neutral: no reading. Tested red to neutral: In a split second "FFFZZZZ!"
and the wire inside the insulated test lead fried and shot out of the
test probe.

Needless to say I didn't get a chance to check 120 to 120. :cool:

Did all the safety stuff right, as far as I know: Insulated (rubber
sole) boots, still stood on a wooden frame instead of the concrete
floor, had someone else on hand tripping the breaker, insulated test
leads - of course. In other words, I came out of it uninjured.

Still, the circuit breaker didn't trip...

What does this mean? Ground fault problem somewhere in the 240v between
the panel and the outlet? Want to know before the electrician comes in
so we understand what he's checking and fixing.

Rick
 
J

James Sweet

Jan 1, 1970
0
Set the meter to AC 750v range. Closed the breaker. Tested black to
neutral: no reading. Tested red to neutral: In a split second "FFFZZZZ!"
and the wire inside the insulated test lead fried and shot out of the test
probe.


Did you have the probe plugged into the Amps jack? I'm not sure how else the
wire would have burned up like that, you may well need a new meter now
though.
 
W

William Sommerwerck

Jan 1, 1970
0
Set the meter to AC 750V range. Closed the breaker. Tested
black to neutral: no reading. Tested red to neutral: In a split
second "FFFZZZZ!" and the wire inside the insulated test lead
fried and shot out of the test probe.

Non-sequitur. It sounds as if you had the probes inserted in the current
jacks.
 
R

Rick

Jan 1, 1970
0
William said:
Non-sequitur. It sounds as if you had the probes inserted in the current
jacks.

Nope. I checked it twice before testing. And since it was brought up I
looked at the meter again - correct jacks.

Your reasoning wouldn't explain why it didn't 'zap' when testing the
first 120v side of the 240v receptacle. I got no reading at all on the
white and black side. (No fried test lead either.) It went 'zap' when I
tested the white and red side.

Rick
 
W

William Sommerwerck

Jan 1, 1970
0
Rick said:
Nope. I checked it twice before testing. And since it was brought up I
looked at the meter again - correct jacks.
Your reasoning wouldn't explain why it didn't 'zap' when testing the
first 120v side of the 240v receptacle. I got no reading at all on the
white and black side. (No fried test lead either.) It went 'zap' when I
tested the white and red side.


But black to neutral might be little or no voltage. Maybe.

Regardless, voltage ranges have extremely high impedances. It should be
"impossible" to pump enough current through them to blow up the wiring.
 
C

CJT

Jan 1, 1970
0
Rick said:
Nope. I checked it twice before testing. And since it was brought up I
looked at the meter again - correct jacks.

Was it set to read voltage or current? Likely current.
 
M

Mr. Land

Jan 1, 1970
0
Did you have the probe plugged into the Amps jack? I'm not sure how else the
wire would have burned up like that, you may well need a new meter now
though.

I think he needed a new meter before he started!

OP, is that the only meter you have? (Er, had?) Starting to sound
like the meter was defective!
 
M

me

Jan 1, 1970
0
I think he needed a new meter before he started!

OP, is that the only meter you have? (Er, had?) Starting to sound
like the meter was defective!

It's been sounding like the operator is defective....
 
S

Sam Goldwasser

Jan 1, 1970
0
But black to neutral might be little or no voltage. Maybe.

Huh?

Black-white should be 115 VAC
Red-white should be 115 VAC
Black-red should be 230 VAC

White-green or white to bare may be near 0 VAC>

Assuming it wired with proper color code.

If white-black was 0 V, then there is a problem. But sounds more like
the meter was on the wrong range, connected wrong, or broken.
Regardless, voltage ranges have extremely high impedances. It should be
"impossible" to pump enough current through them to blow up the wiring.

Yep, something is fishy....

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.
 
R

radiosrfun

Jan 1, 1970
0
Sam Goldwasser said:
Huh?

Black-white should be 115 VAC
Red-white should be 115 VAC
Black-red should be 230 VAC

White-green or white to bare may be near 0 VAC>

Assuming it wired with proper color code.

If white-black was 0 V, then there is a problem. But sounds more like
the meter was on the wrong range, connected wrong, or broken.


Yep, something is fishy....

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above
is
ignored unless my full name AND either lasers or electronics is included
in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.

I personally don't mind checking voltages and so on - "always" double
checking meter settings before hand - even if doing a "radio" or some other
appliance. Going with what Sam mentioned - "Assuming" the wiring is to
proper color code. There are a lot of wannabe Electricians out there - who
don't know their butt hole from a hole in the ground. I can also wonder
about some so-called "electricians". WHY? I've known of at least a dozen
so-called "electrical fires" - occurring not too long after the building was
"re-wired". Obviously - someone must have goofed.

This thread - due to "wiring issues" in the "box" - is starting to mirror
the one about someone's TV set damaged by "alleged" faulty wiring.

I knew a "Mill" Electrician at one time. He had a weird way of wiring
things - and most anyone who knew him would say that. I seen a sample of
"Switch box" wiring he did once for a PA system. Man, what a rats nest. How
it worked is beyond me - but it did. I'm glad I wasn't the one who had to
replace it all - when it was done. The best thing there - would have been to
take it all out and start fresh.
 
D

DaveM

Jan 1, 1970
0
Sam Goldwasser said:
Huh?

Black-white should be 115 VAC
Red-white should be 115 VAC
Black-red should be 230 VAC

White-green or white to bare may be near 0 VAC>

Assuming it wired with proper color code.

If white-black was 0 V, then there is a problem. But sounds more like
the meter was on the wrong range, connected wrong, or broken.


Yep, something is fishy....

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/


Yep, something is fishy, and I suspect the wiring in the receptacle. A few
years ago, I had a dryer that kept burning out heating elements, the temp inside
the dryer would get scorching hot, and if I didn't keep a close watch on it,
would burn the clothes.
Since the dryer was about 20 years old, I bought a new dryer. After a while,
the new dryer started acting the same as the old one. Digging into the problem,
what I found was that the 10ga wiring in the box was too short to fit properly
into the receptacle. One of the wires was barely touching the receptacle screw.
After a lot of tugging and cursing, I finally pulled enough of the wire into the
box to make proper connections. Been working like a champ since.

If the OP's probe got zapped just by inserting it into the receptacle, I can
only surmise that the receptacle was broken and the internal contacts were loose
inside. Plugging the probe into the socket moved the terminals enough that they
shorted.

At any rate, the solution is to replace the receptacle, taking lots of care for
safety's sake, and be sure it's wired correctly.

--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

"In theory, there isn't any difference between theory and practice. In
practice, there is." - Yogi Berra
 
J

James Sweet

Jan 1, 1970
0
Yep, something is fishy, and I suspect the wiring in the receptacle. A
few
years ago, I had a dryer that kept burning out heating elements, the temp
inside the dryer would get scorching hot, and if I didn't keep a close
watch on it, would burn the clothes.
Since the dryer was about 20 years old, I bought a new dryer. After a
while, the new dryer started acting the same as the old one. Digging into
the problem, what I found was that the 10ga wiring in the box was too
short to fit properly into the receptacle. One of the wires was barely
touching the receptacle screw. After a lot of tugging and cursing, I
finally pulled enough of the wire into the box to make proper connections.
Been working like a champ since.

If the OP's probe got zapped just by inserting it into the receptacle, I
can only surmise that the receptacle was broken and the internal contacts
were loose inside. Plugging the probe into the socket moved the terminals
enough that they shorted.

At any rate, the solution is to replace the receptacle, taking lots of
care for safety's sake, and be sure it's wired correctly.


He said the wires to the probes melted. The *only* way this can happen is a
short within the meter itself. Otherwise there's just no way to get enough
current to flow, most DMMs have an impedance of 20 megohms.
 
T

Tim

Jan 1, 1970
0
He said the wires to the probes melted. The *only* way this can happen is a
short within the meter itself. Otherwise there's just no way to get enough
current to flow, most DMMs have an impedance of 20 megohms.
Unless it was on a high amps range, which would have been shunted.

- Tim -
 
J

James Sweet

Jan 1, 1970
0
Unless it was on a high amps range, which would have been shunted.


Well he also said the probes were plugged into the volts jacks, so either
the meter is shorted, or he misread the labels.
 
P

PeterD

Jan 1, 1970
0
Well he also said the probes were plugged into the volts jacks, so either
the meter is shorted, or he misread the labels.

Or he had it set to ohms... And the fuse was either bypassed, or never
existed (like in most *cheap* DVOMs)
 
C

CJT

Jan 1, 1970
0
James said:
Well he also said the probes were plugged into the volts jacks, so either
the meter is shorted, or he misread the labels.
Most meters have several current ranges that _don't_ use the separate
high amps jack.
 
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