Dryer using double rated wattage

[Flicker Index]

While determining how to size a solar system for a new customer, it was discovered that their electric clothes dryer is pulling over 10kVA. The nameplate says it's rated at 5,300 watts. What would cause this issue? It's a brand new dryer. I haven't tested anything on site, wattage measurement is from a Sense monitor, using the "watt check" feature for this appliance.

A lot of people have electric water heater as well as electric dryers. They both use resistive heating and wattage can be similar.
Since washing clothes uses heated water, it triggers the water heater. Because people wash clothes, then dry, the two loads tend to come back-to-back or often overlap. Water heaters are 4.5-5.5kW range, so it seems likely the educated guess made by the software wasn't able to correctly guess the two loads.

The principle is similar to knowing who just left/came home based on the established pattern of time of day it usually happens and the way their car sounds without seeing it and knowing the way their vehicles sound.

 

[Jraef]

The 'sense' system uses 2 CTs on the incoming service lines, and 2 potential measurements from the circuit breaker supplying the unit, to measure the _total_ power consumption of the panel. It then uses pattern recognition to try to recognize the various loads that are running.

So yes, it is measuring each leg and then adding them together...but it is also then trying to use pattern recognition to discern the individual loads from the total of all running loads. As I recall it did a pretty good job of recognizing some things, but some stuff never got recognized.

I don’t see how it could differentiate a dryer heating element from a water heater heating element from an oven heating element…

 

[winnie]

I don’t see how it could differentiate a dryer heating element from a water heater heating element from an oven heating element…

I'm guessing that it 'sees' the combination of the dryer heating element and the motor, and that it 'looks' different from a pulse modulated oven heating element, which 'looks' different from a slowly modulating water heating element.

I was surprised at how well the pattern recognition did, but frustrated by the ways the pattern recognition did not work. In particular I wanted to know how long my oil burner was running, and the system confused the oil burner with the basement dehumidifier. The system easily recognized the clothes dryer...but I don't have an electric stove or water heater, so I couldn't tell you how it did differentiating those.

Eventually I moved to a different system with separate CTs for individual circuits.

-Jonathan

 

[Flicker Index]

I don’t see how it could differentiate a dryer heating element from a water heater heating element from an oven heating element…

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This depends on the bandwidth of the CT as well, but universal motor has a different acoustic/spectrum signature than a heating element.
You can listen to a drill being used and guess about the load being put on.

If you feed the voltage across the shunt running a corded drill through a capacitor (to remove the 120Hz component) and into an earphone, you will be able to "hear" the drill spinning up, or if it's straining on load. This derived signal will sound "motor ish" Try it!

So, when a dryer is started, you will have a current waveform across L-N that represents the acoustic signature of the drum motor. When this comes on simultaneously with a L-L heater load, this gives you an educated guess that it's a dryer coming online. However, the drum motor is always-on through the whole cycle. So, once it's online, you wouldn't be able to tell the 4.5kW dryer heater cycling from a 4.5kW water heater cycling.

 

[hbiss]

While determining how to size a solar system for a new customer, it was discovered that their electric clothes dryer is pulling over 10kVA.

You should know that that's not possible. Measure it yourself with a clamp on meter then tell the customer that this is what you get from techi toys.

-Hal

 

[kwired]

I don’t see how it could differentiate a dryer heating element from a water heater heating element from an oven heating element…

The dryer element might be 5000-5500, the water heater likely 4500, oven element probably 3000 to 4000. So there is some fair chance it can differentiate. But if you have some other load that is nearly identical VA to one of those items - it may not be able to do so.

 

[micabay]

Its been years since I worked on an electric residential dryer but years ago they used a 120 volts for the for the motor, drum light & controls so when everything is running one of the two energized wires would draw several more amps. Could never understand how the NEC allowed electric dryer manufacturers use the ground wire to provide a grounded conductor to power a 120 foot motor, drum light & controls. Should have used a 240 volt motor and a step down transformer for controls & drum light. That would be cheaper then having to use expensive 10/3 NMB cable and a four wire receptacle. now with low current LED'S manufacturers could get a way with 40 VA transformer ( use a 240 volt ignitor ).

Dryers do not use any current to ground. Never have. What you may have experienced was an electrician that installed a circuit to the dryer that didn't have a neutral, and used the ground instead of installing the correct conductors. American dryers are rated for 240/120vac.

 

[kwired]

Dryers do not use any current to ground. Never have. What you may have experienced was an electrician that installed a circuit to the dryer that didn't have a neutral, and used the ground instead of installing the correct conductors. American dryers are rated for 240/120vac.

They were however once permitted to use one conductor for grounded circuit conductor as well as equipment grounding, and still are for existing installations where it was permitted at time of installation, which depending on circumstances can put neutral current over non intended paths.

 

[garbo]

Dryers do not use any current to ground. Never have. What you may have experienced was an electrician that installed a circuit to the dryer that didn't have a neutral, and used the ground instead of installing the correct conductors. American dryers are rated for 240/120vac.

If you only have two energised conductors and a bare ground wire the 120 volt dryer motor, 120 volt drum light bulb and controls all use the ground wire as a neutral.

 

[Little Bill]

If you only have two energised conductors and a bare ground wire the 120 volt dryer motor, 120 volt drum light bulb and controls all use the ground wire as a neutral.

This was never allowed. What was allowed was the neutral could also be used as the ground. The neutral could be bare, IF the conductors were from an SE type cable and originated from the main panel. Otherwise, any cable not being SE, with a bare ground, could not be used, as the ground was never allowed to serve as the neutral. I've encountered many NM XX-2 cables with a bare ground being used on dryers. This was not correct, or allowed if inspected.

 

[LarryFine]

This was never allowed. What was allowed was the neutral could also be used as the ground. The neutral could be bare, IF the conductors were from an SE type cable and originated from the main panel. Otherwise, any cable not being SE, with a bare ground, could not be used, as the ground was never allowed to serve as the neutral. I've encountered many NM XX-2 cables with a bare ground being used on dryers. This was not correct, or allowed if inspected.

Agreed. One thing that was allowed was a 10/3 w/out ground.

 

[Jraef]

Agreed. One thing that was allowed was a 10/3 w/out ground.

But also, sometimes people used SEU cable and the neutral looks like a ground conductor to those not familiar.

 

[kwired]

But also, sometimes people used SEU cable and the neutral looks like a ground conductor to those not familiar.

Looks like a ground, feels like a ground, current flows same way on a conductor whether it has a covering or not and regardless what color that covering may be, but NEC says a bare conductor in SE cable is different than a bare conductor in most any other wiring method.




Add: About had to be manufacturer involvement in determining the rules here to sell product at some point.

 

[Hv&Lv]

I installed the sense monitor myself. But the CT's go on the main service feeder, so it is possible that it is picking up on other loads, not just the dryer. It's supposed to be smarter than that, so I was giving it the benefit of the doubt. I thought I would ask here, in case it is right, so I know what/how to test when I get back on site.

Check to make sure the CTs are oriented correctly.
If one dot is to load and other dot to line, it will double the readings

 

[garbo]

NEC did not allow manufacturers to do this. What they did allow for some time is using the grounded conductor to bond to the frame of the applinance instead of a separate EGC. Nothing wrong with multiwire circuit - we do that with services, feeders and some of us do (or at one time before code made it less practical did run) MWBC's.

It was manufacturers along with listing standards that allowed the multiwire supply to these, code allowed them because they are listed that way.

My best guess and maybe was more of a plus for the manufacturers long ago than it may be today was they could manufacture both gas and electric appliances that utilize the same 120 volt control timers and drive motors and not have as many different parts in inventory to make these appliances.

Kind of no different than GM having the same basic block of a 350 cubic inch engine being placed as the standard engine in a wide variety of vehicles over several years. Some those vehicles also had many other parts that were the same thing across several models over a given time frame.

Was taught that grounded conductors all have insulation except for the SEU service cable, so if it's bare like a bare wire inside if 10/2 NM cable to my thinking its a ground wire.

 

[kwired]

Was taught that grounded conductors all have insulation except for the SEU service cable, so if it's bare like a bare wire inside if 10/2 NM cable to my thinking its a ground wire.

You can have bare grounded service conductor in any wiring method. Aluminum can be the exception, particularly if underground, but bare aluminum isn't allowed underground for any purpose, it simply won't last.