Question ????

[Charley L. Bottger]

Originally Posted by gwells

Yes, I was. All kidding aside, I do use my fingers and hands as Roy does but I also take safety very seriously. I've had a few close calls that would have been much worse had it not been for good safety practices.

I once hired an electrician who thought he would never work again after an accident. He spent more than a year in the hospital and underwent multiple surgeries after being burned by an arc flash. It was not his fault. The accident was long before the current standards of protective gear. He was racking out a breaker and the shutters failed. The explosion that resulted almost killed him.

Whenever I had careless electricians who needed to learn to be more safe, I made them work with Jim B. Jim could hardly move as a result of his accident. He was the slowest electrician I have ever hired but one of the most valuable. Everyone who worked with Jim respected him and came away from the experience with a new appreciation for safety procedures and equipment.

I have some very vivid memories also of a near miss on a 750 ton chiller that operated on high voltage don't remember the exact voltage somewhere above 1200 volts but the MCC exploded right before my arrival to start up the chiller the front cover was bolted into place and it blew the front panel about 50 feet across the equipment room and I very well could have been in its path if I had been in the building a little earlier so I remember the power of a arc flash first hand nothing to fool around with

[Sean Fogarty]

What happened to the original question??

[Charley L. Bottger]

Originally Posted by sfogarty

What happened to the original question??

It got answered numerous post back

[Bob Elliott]

Was there an answer.I missed it.
Seems above and beyond home inspection.
Mine take 4 hours as it is.Might as well run diagnostics on the kitchen appliances while at it.

[Robert J. OConnor]

Originally Posted by rcooke

When I started the trade I was taught to always use you left hand to throw a disconnect.

And there is a reason why old school electricians walk around with one hand in their pocket ...

Originally Posted by gwells

As both Jim and Robert have said, there could be an appreciable imbalance on an electric dryer.

The amount of the imbalance is inversely proportional to the temperature setting. The lower the temperature setting, the greater the imbalance. Dryers also have a No Heat mode which results in a 100% imbalance.

Just to clarify, I didn't mean to imply that the 240V heating element was the source of the imbalanced load ... just that when you add that to the 120V dryer motor you get an imbalanced load.

The imbalanced load on a dryer circuit is a result of the 120V load on the dryer motor. Both hot wires will have the same current from the 240V heating elements, and one of the hot wires and the neutral wire will have current from the 120V motor. The imbalance from the motor on one of the hot wires will be the same regardless of the temperature setting.

[Roy D. Cooke, Sr]

Originally Posted by roconnor

And there is a reason why old school electricians walk around with one hand in their pocket ...

.

Good one I forgot that yes that was part of the teaching a long time ago Thanks for the memory .
The Trade treated me well and I met a lot of great people.
25 Cycle was in all homes and plants when I started the trade .
They where just converting to 60 cycle in Ontario.

Roy

[George P. Wells, CMI]

Originally Posted by roconnor

Just to clarify, I didn't mean to imply that the 240V heating element was the source of the imbalanced load ... just that when you add that to the 120V dryer motor you get an imbalanced load.

The imbalanced load on a dryer circuit is a result of the 120V load on the dryer motor. Both hot wires will have the same current from the 240V heating elements, and one of the hot wires and the neutral wire will have current from the 120V motor. The imbalance from the motor on one of the hot wires will be the same regardless of the temperature setting.

Robert,

I understood what you meant to say in your original comment regarding the heating element. I realize you understand exactly what is going on but for the benefit of those who may be confused, I'll explain further.

The current flowing through the motor does not change as the temperature setting of the dryer changes but the ratio of current flowing between the ungrounded legs changes. If the temperature is set to No Heat, there is no current flowing through the heating elements but current is flowing through the motor. So, while the current flowing through the motor is relatively constant, the ratio between the legs is infinitely high when the motor is on and the heating element is off.

Let's apply some numbers to the explanation. Before I continue, please bear in mind that neither the numbers I am going to use are real nor are the operating conditions real. They are for illustration only.

Suppose that the motor draws 10 Amperes but is not running and that there is one 240V heating element that is energized and drawing 20 Amperes. The ratio between the legs is 1:1. The circuit is balanced.

Turn the motor on and leave the heating element on. We now have 20 amperes flowing on one leg, 30 Amperes flowing on the other leg and 10 Amperes (the difference between the legs) flowing on the grounded conductor. The ratio between the ungrounded legs is now 1.5:1. Finally, turn the heating element off and leave the motor on. The ratio between the ungrounded legs is now ∞. Therefore, the ratio between the ungrounded legs is inversely proportionate to the heat setting. As you said, the difference in current flow between the two ungrounded legs is equal to the current flowing through the motor.

I chose to incorporate the current ratio between the ungrounded legs in my explanation because I wanted to explain how the ratio in temperatures can be different and can vary at the terminals of a 240V breaker but still be normal.

[Charley L. Bottger]

Originally Posted by belliott

.Might as well run diagnostics on the kitchen appliances while at it.

I do that also and if you would quit eating those dumb hot dogs you could move a little faster and not take you 4 hours for a 3 hour job

I have some more pics to post from today's inspection will do it later

[Robert J. OConnor]

Originally Posted by gwells

The current flowing through the motor does not change as the temperature setting of the dryer changes but the ratio of current flowing between the ungrounded legs changes ... the ratio between the ungrounded legs is inversely proportionate to the heat setting.

The ratio of current between the ungrounded legs would only be inversely proportional to the heat setting when referenced to one of the ungrounded legs (A/B), and would be directly proportional to the heat setting when referenced to the other ungrounded leg (B/A).

Now if you changed that to a load difference/leg reference and take the magnitude of the unbalanced load (Δ) and divide that by the RMS current in either of the ungrounded legs (A or B), the load difference/leg ratio will increase as the heat setting decreases (Δ/A or Δ/B) and thus would indeed be inversely proportional to heat setting over limited load ranges.

However the ratios are variable depending on the ungrounded leg referenced, there are no generally accepted or standard industry reference points or procedural methods for proportional imbalance or current difference ratios, the inverse using either non-standardized method becomes undefined at the no-load heat setting for one of the ungrounded legs, and it would be intrinsically implied that the magnitude of the unbalanced load in absolute terms is directly or indirectly related to the heat setting which is counterintuitive ...
.

Couldn't resist ... how about we just refer to unbalanced load in terms of Amps, which also relates to temperature difference ...

[Charley L. Bottger]

Originally Posted by roconnor

The ratio of current between the ungrounded legs would only be inversely proportional to the heat setting when referenced to one of the ungrounded legs (A/B), and would be directly proportional to the heat setting when referenced to the other ungrounded leg (B/A).

Now if you changed that to a load difference/leg reference and take the magnitude of the unbalanced load (Δ) and divide that by the RMS current in either of the ungrounded legs (A or B), the load difference/leg ratio will increase as the heat setting decreases (Δ/A or Δ/B) and thus would indeed be inversely proportional to heat setting over limited load ranges.

However the ratios are variable depending on the ungrounded leg referenced, there are no generally accepted or standard industry reference points or procedural methods for proportional imbalance or current difference ratios, the inverse using either non-standardized method becomes undefined at the no-load heat setting for one of the ungrounded legs, and it would be intrinsically implied that the magnitude of the unbalanced load in absolute terms is directly or indirectly related to the heat setting which is counterintuitive ...
.

Couldn't resist ... how about we just refer to unbalanced load in terms of Amps, which also relates to temperature difference ...

Smart Butt ya know in Oklahoma we don't allow PE's to have a pencil until they have worked in the field at least 5 years

[Robert J. OConnor]

Originally Posted by cbottger

Smart Butt ya know in Oklahoma we don't allow PE's to have a pencil until they have worked in the field at least 5 years

Yup, same here ... spent a good 5 years in the field and also doing calculations by hand before they would even let me touch a programmable calculator or a computer ... Have quite a bit more practical experience on top of that, but can still crunch the numbers/theory when I need to ...

[Larry Simpson]

Originally Posted by cbottger

I have some very vivid memories also of a near miss on a 750 ton chiller that operated on high voltage don't remember the exact voltage somewhere above 1200 volts but the MCC exploded right before my arrival to start up the chiller the front cover was bolted into place and it blew the front panel about 50 feet across the equipment room and I very well could have been in its path if I had been in the building a little earlier so I remember the power of a arc flash first hand nothing to fool around with

I couldn't even begin to tell you all how many times I've had a near miss with electricity. There are a lot of older homes in my area with some really bad wiring, most of them are either K&T or cloth-covered. I have no idea how any of those places are still standing.

It can be a bit scary climbing around in an attic of one of those older houses. They are usually old, dark and dusty. That makes it really hard to see anything up there, much less a wire that may or may not still have a cloth wrap. Safety is important!

[Jimmy D. Smith]

Originally Posted by cbottger

Should I or would you be concerned about a 10 degree temp differential between the two legs on a 240 volt double pole breaker Yes or no please

Depends on the load at the time of measurement. If only at half load for example, at full load the temp would be closer to 40. You also did not give the units, so if this is 10C, it would be a bigger concern.
Short answer is probably yes, but more information is required for definate answer.

Jimmy

[KEVIN WOOD]

Thats what I get for going out of town for 1/2 the day.
Nice discussion. I have a friend that lost both arms up to the elbow when he worked in the Steel Plant. There are many other accidents that have occured and now they have safety meetings every week. Too bad for those that have died but good news for the rookies.
Nice to see you back on the MB again Roy, I new you would be back soon!