Motor slowing when electric dryer comes on

[Graven Water]

I have an air turbine running in my house, and it slows down when the
electric dryer is turned on. Even though the air turbine is on a
different circuit from the electric dryer. The same happens when any
other appliance in my house that uses a lot of power, goes on.

My electrician came by to check it out, tightened connections in the
circuit breaker box, but it didn't help.
He's not sure why this is happening. The turbine draws about 3 amps.
Any ideas?

tia
Laura

 

[Graven Water]

What is the thing you called a turbine,

It's like a fan but more powerful, it's part of an airline respirator so
it has to push air through many feet of hose. It uses a universal motor,
and the speed can be varied by a rheostat.

Can you notice any lights diming or getting brighter when you hear the
turbine slow down?

No, but I use fluorescent lights. I don't think they would do that. The
electrician was asking me the same kind of questions.

I tried connecting the turbine to various outlets in my house and the
same thing happens - other appliances lower the turbine's speed even if
they aren't on the same circuit.

Laura

 

[Winston]

Graven Water wrote:

(...)

I tried connecting the turbine to various outlets in my house and the
same thing happens - other appliances lower the turbine's speed even if
they aren't on the same circuit.

Did you see Dave Platt's response?
He hit it on the head, IMHO.

--Winston

 

[Winston]

It might be an idea to try another 'leccy
If they can't pick volt drop they should stay chasing walls
and running conduit.

la La LA La la I cannnnt hearrr youuuuu!



--Winston

 

[Franc Zabkar]

A failing "master" circuit breaker in the breaker box might have the
same effect.

I would think that high resistance in the breaker would quickly result
in its failure. If the voltage drop were around 5V, then at 3A the
dissipation in the breaker would be 15W. And that's only taking the
motor into account, not the dryer.

- Franc Zabkar

 

[Graven Water]

My electrician came over to check it out more thoroughly.
He measured voltage at circuit the turbine is on, when I turned the dryer
off and on. The voltage only dropped a small amount. I think he said by
2 volts. (earlier on, he measured the current draw, and didn't see a
change)

But, it noticeably affected the turbine's speed. Earlier, I checked what
the turbine speed was doing, with an airflow meter, and when the dryer was
turned on, the airflow goes down about 5%. I've noticed the airflow going
down much worse than that, at other times.

For some reason, the turbine is very sensitive to a slight change in
voltage.

He also checked the voltage before and after the main circuit breaker, and
it went down by 4 volts when the dryer goes on, both before and after.

So, he said there's a problem with the utility co's equipment, like maybe
a failing transformer, but right now it's a minor problem. I hope
the utility co. will fix it.

Maybe the fact that turning on the dryer affects the turbine speed much
worse sometimes, means that the problem with the utility co's equipment
is erratic.

Laura

 

[tm]

My electrician came over to check it out more thoroughly.
He measured voltage at circuit the turbine is on, when I turned the dryer
off and on. The voltage only dropped a small amount. I think he said by
2 volts. (earlier on, he measured the current draw, and didn't see a
change)

But, it noticeably affected the turbine's speed. Earlier, I checked what
the turbine speed was doing, with an airflow meter, and when the dryer was
turned on, the airflow goes down about 5%. I've noticed the airflow going
down much worse than that, at other times.

For some reason, the turbine is very sensitive to a slight change in
voltage.

He also checked the voltage before and after the main circuit breaker, and
it went down by 4 volts when the dryer goes on, both before and after.

So, he said there's a problem with the utility co's equipment, like maybe
a failing transformer, but right now it's a minor problem. I hope
the utility co. will fix it.

Maybe the fact that turning on the dryer affects the turbine speed much
worse sometimes, means that the problem with the utility co's equipment
is erratic.

Laura

Maybe the dryer is creating a vacuum in the room? Making the turbine load
greater or less?

 

[[email protected]]

My electrician came over to check it out more thoroughly.
He measured voltage at circuit the turbine is on, when I turned the dryer
off and on. The voltage only dropped a small amount. I think he said by
2 volts. (earlier on, he measured the current draw, and didn't see a
change)

But, it noticeably affected the turbine's speed. Earlier, I checked what
the turbine speed was doing, with an airflow meter, and when the dryer was
turned on, the airflow goes down about 5%. I've noticed the airflow going
down much worse than that, at other times.

For some reason, the turbine is very sensitive to a slight change in
voltage.

He also checked the voltage before and after the main circuit breaker, and
it went down by 4 volts when the dryer goes on, both before and after.

So, he said there's a problem with the utility co's equipment, like maybe
a failing transformer, but right now it's a minor problem. I hope
the utility co. will fix it.

Maybe the fact that turning on the dryer affects the turbine speed much
worse sometimes, means that the problem with the utility co's equipment
is erratic.

Laura

4 volts is a major drop for a relatively minor load. Typically a
clothes dryer is on a 30 amp circuit, but draws somewhat less. An
electric range or cental air conditioner is typically on a 50 amp
circuit.

Since the voltage drop is occurring at the hot side of the main
breaker, it's the electric companies responsibility. It COULD be the
lugs on the input to the circuit breaker, it could be in the meter box
itself, or it could be somewhere upstream.

PlainBill

 

[Graven Water]

4 volts is a major drop for a relatively minor load. Typically a
clothes dryer is on a 30 amp circuit, but draws somewhat less. An
electric range or cental air conditioner is typically on a 50 amp
circuit.

Is it a fire hazard?
Laura

 

[[email protected]]

Is it a fire hazard?
Laura

Good question, let's do some 'back of the envelope' calculations. The
tests the electrician made indicates the problem is BEFORE the main
circuit breaker. If the entire 4 volt drop occurs at a single point,
and the actual dryer load is 25 amps, that means 100 watts is being
dissipated. Of course, since the dryer represents only a fraction of
the actual maximum load, the power dissipated is much greater. If the
power is being dissipated at a single point (a poorly tightened
connector), it could POSSIBLY lead to a fire. It is far more likely
that the eventual result will be a complete failure of the connector.

Here's my analysis: The voltage drop could be occuring in the wires
from the main breaker back to the meter, in the wires from the meter
back to the local transformer, or at the connectors in the breaker
box, meter housing, or local transformer. If it's occurring in the
wires, it's due to physical damage; those wires should be rated for at
least 150 amps. Barring physical damage to the wires, the problem is
at one of the connectors.

It's unlikely the problem is occurring at the connectors on the main
breaker, think of how much heat is given off by a 100 watt light bulb.
A self-aware electrician should have noticed the heat. It could be in
the power meter housing, but my suspect would be at the local
transformer. And that is big enough, and runs hot enough that an
extra 100 watts isn't noticeable.

PlainBill

 

[Graven Water]

4 volts is a major drop for a relatively minor load. Typically a
clothes dryer is on a 30 amp circuit, but draws somewhat less. An
electric range or cental air conditioner is typically on a 50 amp
circuit.

The utility co. came out, a crew replaced some wire that they said was very old.
After changing the wire,
they checked line voltage when I turned the microwave off and on. The
voltage went down from 243 something to 240.8 when the microwave was on,
it uses a KW.
But, the utility co. guy said a 2-volt drop when the microwave goes on,
isn't a problem! He said, you get 240 volts and that's what we promise.
My dryer is broken, the on-switch died, so I couldn't test voltage change
with the dryer on.
So, IS there a problem with the wiring upstream of the meter?
I tried plugging the air turbine into various
circuits. On many of those circuits, the turbine would slow down when the
microwave went on. Right now I have it plugged into a circuit where the
microwave doesn't slow the turbine.
The utility guy said they'd put a recording voltmeter on the meter. Which
seems sensible.
The voltage did drop to 238 volts previously when the dryer went on. So
that's below 240.
I hate it when this sort of confusing stuff happens. I don't know who is
right.
Laura

 

[[email protected]]

The utility co. came out, a crew replaced some wire that they said was very old.
After changing the wire,
they checked line voltage when I turned the microwave off and on. The
voltage went down from 243 something to 240.8 when the microwave was on,
it uses a KW.
But, the utility co. guy said a 2-volt drop when the microwave goes on,
isn't a problem! He said, you get 240 volts and that's what we promise.
My dryer is broken, the on-switch died, so I couldn't test voltage change
with the dryer on.
So, IS there a problem with the wiring upstream of the meter?
I tried plugging the air turbine into various
circuits. On many of those circuits, the turbine would slow down when the
microwave went on. Right now I have it plugged into a circuit where the
microwave doesn't slow the turbine.
The utility guy said they'd put a recording voltmeter on the meter. Which
seems sensible.
The voltage did drop to 238 volts previously when the dryer went on. So
that's below 240.
I hate it when this sort of confusing stuff happens. I don't know who is
right.
Laura

Understand that the home electrical system is fed by a center tapped
secondary of a step down transformer. The center tap is neutral, and
is tied to earth ground at your breaker box. The voltage from either
end of the secondary to the center tap is nominally 120 volts (it may
drop under load). The voltage from one end of the secondary to the
other is 240 volts. The typical outlet is wired from the center tap to
one of the ends, the dryer is wired across both ends.

It would be interesting to know if the voltage from the center to each
side drops the same amount when the dryer is running.

One relatively simple test you can do. You have identified at least
one circuit where the turbine is not affected by the microwave. It
would be interesting to know if that circuit is affected by the dryer.

PlainBill

 

[Carolee]

I have an air turbine running in my house, and it slows down when the
electric dryer is turned on. Even though the air turbine is on a
different circuit from the electric dryer. The same happens when any
other appliance in my house that uses a lot of power, goes on.

My electrician came by to check it out, tightened connections in the
circuit breaker box, but it didn't help.
He's not sure why this is happening. The turbine draws about 3 amps.
Any ideas?

tia
Laura

When my oven comes on my kitchen light dims for about 1 second so does
that mean I have to call 9-1-1 now? You stupid bitch.

 

[Paul Drahn]

The utility co. took down their recording voltmeter. It was on the
weatherhead, on my roof where the power line is attached.

I talked to an engineer at the utility co. today, and he said
everything is fine with my voltage. He said it's between 120 and 124
volts usually, he saw one time it went down to 115 volts.

The only thing he noticed was that the load is somewhat unbalanced,
like 25 amps on one leg and 10 amps on the other, usually.

Could an unbalanced load cause voltage fluctuations?

One day when I was doing my laundry and the heat pump may have been
working hard, he said the load went up to 55 amps. I don't know if
this could cause flaky voltage inside my house, it's 100-amp service.

I might borrow or buy a voltmeter, and see whether voltage at the
outlet correlates with the drastic fluctuations in airflow that I've
noticed.

I doubt it's the fault of the motor volume control, because the
airflow goes up rather predictably at night.

And like I said, when I use the electric dryer, the airflow
predictably goes down, sometimes a lot.

Maybe there's something other than just voltage that might be
affecting the turbine speed. Some other power quality issue, perhaps.

Laura

Any chance you share the power transformer with other houses? If so,
their use will have a noticeable effect on your voltage with only a 100
amp service.

Paul

 

[Paul Drahn]

There are about 6 houses on the same transformer. So if I upgraded
the service, that would help?

Laura

I had to do that last summer as part of a new heat pump with electric
heat backup. Cost $1500 up front for the power company to upgrade the
transformer. There are a total of 3 houses on my transformer.

Where do you live? I am really surprised that the power company would
put 6 houses on the same transformer. Houses must be located pretty
close together.

Paul

 

[Winston]

Phil Hobbs wrote:

(...)

I'm not an electrician, but I believe that most houses in the US have
two-phase service,

Nup. Single phase, center tapped.

http://en.wikipedia.org/wiki/Split-phase_electric_power

and that the neutral is bonded to the ground rod near
the service entrance. Voltage drops in the neutral make one side go down
in voltage and one side go up.

Yup.

--Winston

 

[josephkk]

I'm not an electrician, but I believe that most houses in the US have
two-phase service, and that the neutral is bonded to the ground rod near
the service entrance. Voltage drops in the neutral make one side go
down in voltage and one side go up.

Cheers

Phil Hobbs

That is still single phase service.

?-)

 

[josephkk]

The voltage at the turbine outlet goes up by about 1 volt when the 1
kW microwave goes on. They're on opposite sides of the service. Is
this a significant amount?

It does indicate a problem developing.

?-)

 

[josephkk]

Maybe that's the problem. I get the impression that many of the
changes in speed in the air turbine are being caused by other people's
usage. I live in upstate NY.

So is it possible for an unbalanced load to cause the voltage at an
outlet to be different from what the power co. measures at the
weatherhead?

Only to the extent that the unbalance is internal to your house. Which
may explain all of it or not, seriously have your neutral wiring checked
as well.

?-)