I need to install a 240 V heater (5kw). Owner wants it on a timer so that it only runs at a particular time in the early morning hours.I am debating if I should use a DP/ST time clock(T104) or control it through a definite purpose contactor.Is it common to use time clocks for other than say lighting loads? Rating of clock is 40A, 20A or there abouts will be max draw on the unit. Suggestions appreciated.
Time clock vs contactor
- Thread starter nizak
- Start date
- Status
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
A resistive load like a heater would be a less stressful load than the same wattage of lighting load, since there will be no cold filament or discharged capacitor inrush.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
What does it have for a thermostat? If designed for external thermostat maybe just use a programmable thermostat.
James L
Senior Member
- Location
- Kansas Cty, Mo, USA
- Occupation
- Electrician
You can't "control" a load with a contactor, without some way to control the contactor coil. A contactor simply connects/disconnects the circuit(s) when the coil is energized and de-energized. If there's not something or someone to control the coil, the contactor won't turn on or off.
In a contactor scenario, you would most likely have some form of switching mechanism that is unable to carry the load, like some sort of timer. The timer turns on the coil on the contactor, and the contacts close to make the 2 circuits contact each other to get power to the load.
btw, a Definite Purpose contactor is designed for a definite purpose, as the name indicates. In short, every contactor will be rated to turn on/off so many times before it is subject to fail. A DP contactor will be rated to fail at a much lower number of on/off cycles when compared to better contactors. I don't use them in every-day scenarios. They're the cheapest, noisiest contactors available.
In a contactor scenario, you would most likely have some form of switching mechanism that is unable to carry the load, like some sort of timer. The timer turns on the coil on the contactor, and the contacts close to make the 2 circuits contact each other to get power to the load.
btw, a Definite Purpose contactor is designed for a definite purpose, as the name indicates. In short, every contactor will be rated to turn on/off so many times before it is subject to fail. A DP contactor will be rated to fail at a much lower number of on/off cycles when compared to better contactors. I don't use them in every-day scenarios. They're the cheapest, noisiest contactors available.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
I'm leaning towards programmable stat too - throwing in a DP contactor if necessary.
- Occupation
- Licensed Electrician
I'd likely go with a programmable stat too. There a little pricey but will do what the OP wants, take less time and material than a time clock, and have more flexibility. Better for everybody.
- Location
- Massachusetts
You would need a lighting or heating contactor.
It is a code violtion to use a definite purpose contactor for anything other direct replacement in a factory listed assembly.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
+1 on the no DP contactor issue. DP should be understood to stand for "Don't Purchase" as well as Definite Purpose. They get misused all the time, but a savvy AHJ will bounce you for it, as they should. They are meant for OEMs who time their component failures to their warranty period, then sold later as strictly replacement devices that can only be used in the exact manner in which the OEM intended.
That said, it's easier to swap out a contactor later than a time clock. If the time clock is only switching the contactor coil it may outlive the clock motor or electronics. If it is switching the heater elements themselves, you may be back out there in 5-10 years.
That said, it's easier to swap out a contactor later than a time clock. If the time clock is only switching the contactor coil it may outlive the clock motor or electronics. If it is switching the heater elements themselves, you may be back out there in 5-10 years.
StarCat
Industrial Engineering Tech
- Location
- Moab, UT USA
- Occupation
- Imdustrial Engineering Technician - HVACR Electrical and Mechanical Systems
HVACR Control
HVACR Control
Any heating only unit can be controlled with a timeclock by breaking the " W " wire back to the unit control terminal strip.
This is a 24VAC circuit in most cases of standard old school equipment.
About programmable thermostats.
Yes they " can " work, but in 30 years I have never seen any end user that has a clue how to operate one.
In the 90s I had to keep a library on my Service Truck due to some of the major complexity of the older units which no single mortal person can memorize.
They are all menu driven and the intracacies are major.
The new ones are better but most of them still have a " HOLD " button which will override whatever the current program is.
Programmable stats really only work if they are run by someone who understands them and what they can do. IN those hands they can work well to both save energy during setback and maintain comfort during occupied times. Even then they have to be seasonally adjusted for optimal results.
The advent of Such Thermostats has created untold millions of service calls and wasted countless hours of time.
There are exceptions, but many of them are never used as intended.
They are another Technology that has trapped millions with promises that will never be delivered due to human nature being what it is.
The benefits of digital control and say anti-short cycle protection can be had with a digital NON-Programmable stat.
HVACR Control
Any heating only unit can be controlled with a timeclock by breaking the " W " wire back to the unit control terminal strip.
This is a 24VAC circuit in most cases of standard old school equipment.
About programmable thermostats.
Yes they " can " work, but in 30 years I have never seen any end user that has a clue how to operate one.
In the 90s I had to keep a library on my Service Truck due to some of the major complexity of the older units which no single mortal person can memorize.
They are all menu driven and the intracacies are major.
The new ones are better but most of them still have a " HOLD " button which will override whatever the current program is.
Programmable stats really only work if they are run by someone who understands them and what they can do. IN those hands they can work well to both save energy during setback and maintain comfort during occupied times. Even then they have to be seasonally adjusted for optimal results.
The advent of Such Thermostats has created untold millions of service calls and wasted countless hours of time.
There are exceptions, but many of them are never used as intended.
They are another Technology that has trapped millions with promises that will never be delivered due to human nature being what it is.
The benefits of digital control and say anti-short cycle protection can be had with a digital NON-Programmable stat.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I find those same people that can't understand their programmable thermostat can't understand how to use a fairly simple time clock controller either though, especially if it is electronically programmed as well.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Tangent alert:
Tonight I am driving to my 88yo mother's house to remove her programmable setback t-stat and put in an old fashioned Honeywell Round, but the one they offer now for low vision, with the really big numbers on the dial.
She was constantly overriding the programming anyway, then she couldn't see that she had messed something up and I had to drive 40 miles to put it right... So screw it, if she is going to do it all manually anyway, why bother with the complex stuff? K.I.S.S. :slaphead:
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I've put in a few of those as well. Even the standard "round" is still preferred by a lot of people just because it is simple and has been around long enough most people understand them.
There are also those that don't get the concept of setting the temp where you want and it will get there and will maintain that temp when it does get there, they think if they turn it way up it will get warm faster (and it very well might be a little faster if you have multistage system) but then they forget and get overkill heat and then turn it down way too much and eventually have the opposite effect:slaphead:
- Location
- Windsor, CO NEC: 2017
- Occupation
- Hospital Master Electrician
Uh oh. What section? :ashamed:
- Location
- Massachusetts
It would be a 110.3(B) deal or at least 110.3
They are not listed, only recognized.
http://site.ul.com/global/documents...ors/technical/ul_RecognizedComponentMarks.pdf
jeepx
Member
- Location
- knoxville,tn,united states
after reading the other replies not sure that I seen any bad ideals and I agree programmable anything can be difficult for anyone at times and time consuming to instruct the customer on its use so a simple 24 hour dial type time clock. Controlling a multipurpose contactor with the correct amp rating would seem to be the most practical fit
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Even those are too confusing to some:happyyes:
- Location
- Connecticut
- Occupation
- Engineer
110.3 doesn't require that equipment be listed.
- Status