230 volt heating elements wired in series at 480 volt

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Had a call to a CNC shop with a oil filter pump that had the heater elements fail at about 10 mouths old (this is the second set in 2 years). The elements look like waterheater units but were supplyed by the manufacture of the filtration system. Connected in series at 480 volt but rated at 230 volt, I know ohms law says this will work but can you use a 230 volt device like this? The elements faild in a rupture type manor (split down the length) Said unit is built with this from the factory but seems a little odd to me. Trying to find the manufacture of the elements for there view but have had no luck, anyone ever run into this before?
 

templdl

Senior Member
Location
Wisconsin
Had a call to a CNC shop with a oil filter pump that had the heater elements fail at about 10 mouths old (this is the second set in 2 years). The elements look like waterheater units but were supplyed by the manufacture of the filtration system. Connected in series at 480 volt but rated at 230 volt, I know ohms law says this will work but can you use a 230 volt device like this? The elements faild in a rupture type manor (split down the length) Said unit is built with this from the factory but seems a little odd to me. Trying to find the manufacture of the elements for there view but have had no luck, anyone ever run into this before?

Two 230 elements in series with 480v doesn't seem like any big deal if neither element failed. But if one element fails where it opened circuited instead of having 230 across the failure you would now have 480v. Does that make sense?
 

K8MHZ

Senior Member
Location
Michigan. It's a beautiful peninsula, I've looked
Occupation
Electrician
I used to build ceramic art kilns. Some of the 240 volt kilns used two 120 volt elements in series. Actually, it was quite common as it allowed a single element to serve two or more models. Surprisingly, the connections were not problematic. The elements would usually fail from stuff getting on them or not being supported properly.
 

kwired

Electron manager
Location
NE Nebraska
There are dual voltage elements that do exactly that, series certain segments for the higher voltage and parallel them for the lower voltage.

Is there any method of preventing them from overheating or running "dry"?

Is there by chance a 277 volt neutral connected or any incidental grounding of the midpoint? This would result in operation of each 240 volt rated element @ 277 volts instead of 240, although they still likely would operate for a long time as long as they never operated "dry".
 
This was my first Q to them

This was my first Q to them

The oil is brougt back to the holding tank (pre filter) though a pipe that feeds over both elements and are appox. 2 foot deep in a tank that is 4 foot by 6 foot sqare and 3 foot deep. Both units were made in china ? I think we have some defective units that one fails than takes out the other. The owner says that there is no way that the oil was low (CNC operation that they monitor very close) What is your opinion?
Sounds more like someone let it run dry.
 

kwired

Electron manager
Location
NE Nebraska
After a little thought, I am wondering if these are simply water heater elements, maybe they are not the right thing for the application.


Water is probably a much better conductor of heat and that would mean cooler performance of the element, oil is more resistant to temperature change and would require an element designed to operate at a higher temperature, or it will overheat. Maybe a different element type is needed - or at least lower watt density, or a circulating system to move the oil around faster. Maybe the two elements are too close to each other, making things even worse. Sounding like a possible bad design to start with.
 

mivey

Senior Member
What is the applied voltage while under load? These already have 480 applied to them vs 460, another 10 or 20 volts could be stressing them.
That should not matter if the supply voltages are meeting standards. The maximum range A standard is 504 volts on a 480 volt system. The 230 volt devices are fully rated to handle 252 volts (range A) and that translates to 504 volts on the 480 volt system.

In range B (508 volts max) the devices are required to give acceptable performance if practicable (i.e. they may work but not give full life). Beyond range B there are no requirements for acceptable performance.

If the voltages are staying in range B or beyond, it is a supply problem anyway.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
That should not matter if the supply voltages are meeting standards. The maximum range A standard is 504 volts on a 480 volt system. The 230 volt devices are fully rated to handle 252 volts (range A) and that translates to 504 volts on the 480 volt system.

In range B (508 volts max) the devices are required to give acceptable performance if practicable (i.e. they may work but not give full life). Beyond range B there are no requirements for acceptable performance.

If the voltages are staying in range B or beyond, it is a supply problem anyway.

Can't argue one way or another, just a suggestion. I certainly used a lot of 130v lamps on a 120v circuits that were well within tolerances, to extend the life of them a bit.
 

mivey

Senior Member
Can't argue one way or another, just a suggestion. I certainly used a lot of 130v lamps on a 120v circuits that were well within tolerances, to extend the life of them a bit.
That's true. My voltage usually stays over 120v and the 120v bulbs don't seem to last. I'm sure some of it is a quality issue but I stick with 130v bulbs when I can.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
The oil is brougt back to the holding tank (pre filter) though a pipe that feeds over both elements and are appox. 2 foot deep in a tank that is 4 foot by 6 foot sqare and 3 foot deep. Both units were made in china ? I think we have some defective units that one fails than takes out the other. The owner says that there is no way that the oil was low (CNC operation that they monitor very close) What is your opinion?
They ALWAYS say there is now way it was ever run dry. ALWAYS! Been there several times on similar situations, the last one was on some hydraulic pumps where they said I had hooked up the motors to run backwards because they had no oil pressure, turned out they never filled the reservoir.

What usually happens in cases like this is that when it first arrived, some newbie got excited about his new toy and turned it on without reading the instructions first, and there was no oil in it yet. When he heard the crackling noise from the tank, he immediately shut it down, but by then it was too late, he had cracked the ceramic (or other insulating) coating on the elements. Then when they put in the oil it still worked OK, so he kept his mouth shut. But over time, acids that form in the oil as it ages eat into the resistive wire until it eats through one of them, then it starts to arc, which damages the other at almost the same time.

If you were the guy that did it, would you admit it?
 

kwired

Electron manager
Location
NE Nebraska
They ALWAYS say there is now way it was ever run dry. ALWAYS! Been there several times on similar situations, the last one was on some hydraulic pumps where they said I had hooked up the motors to run backwards because they had no oil pressure, turned out they never filled the reservoir.

What usually happens in cases like this is that when it first arrived, some newbie got excited about his new toy and turned it on without reading the instructions first, and there was no oil in it yet. When he heard the crackling noise from the tank, he immediately shut it down, but by then it was too late, he had cracked the ceramic (or other insulating) coating on the elements. Then when they put in the oil it still worked OK, so he kept his mouth shut. But over time, acids that form in the oil as it ages eat into the resistive wire until it eats through one of them, then it starts to arc, which damages the other at almost the same time.

If you were the guy that did it, would you admit it?
That is understandable at the initial installation, but OP says they have been replaced more than once, is it safe to assume there may be design issues? Simple oil level switch would help with preventing from running dry. I did suggest earlier that if these indeed a water heater element by design that maybe they would not perform as well for heating oil, nobody has replied with any thoughts on that.
 

templdl

Senior Member
Location
Wisconsin
It makes sense...but it is an open circuit ...so it doesn't matter.

If I am to understand you correctly if 480v was applied across (2) 230V heating elements that are connected in series and one of the elements failed and open circuited that you wouldn't have 480v across the open circuit? Interesting.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Hmm, two 240V devices wired in series and then connected to 480V - sure sounds like what is done with normal motor and transformer windings.
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
It makes sense...but it is an open circuit ...so it doesn't matter.

If I am to understand you correctly if 480v was applied across (2) 230V heating elements that are connected in series and one of the elements failed and open circuited that you wouldn't have 480v across the open circuit? Interesting.

I don't think you understand him correctly. I don't see that suggested anywhere.
 

templdl

Senior Member
Location
Wisconsin
I don't think you understand him correctly. I don't see that suggested anywhere.

It's what he didn't say that I'm addressing. "The elements failed in a rupture type manor (split down the length) Said unit is built with this from the factory but seems a little odd to me."
This leads me to believe that the 230v heater failed and that there was 480v applied across the failure which resulted in the failure ending up to be a failure in a rupture type manor.
I you had one 230v heater fail where the element opened you will have 480v across that failure and not 230v which would result in significant more damage.
 
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