nec
- Thread starter newt
- Start date
- Status
- Location
- Windsor, CO NEC: 2023
- Occupation
- Hospital Master Electrician
Great question! I have always switched the line side of the transformer.
But when it comes to dimming, I get a little confused. I'd love to hear others replies about dimming, and types of dimmers, and when to use each different kind.
But when it comes to dimming, I get a little confused. I'd love to hear others replies about dimming, and types of dimmers, and when to use each different kind.
jeff43222
Senior Member
- Location
- Minneapolis, Minnesota
I also switch the line side of the transformer.
As for dimming, apparently low-voltage lights sometimes require a special type of magnetic dimmer. I had to install some recently, and they were very expensive -- $50 each.
As for dimming, apparently low-voltage lights sometimes require a special type of magnetic dimmer. I had to install some recently, and they were very expensive -- $50 each.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
From a pure energy savings standpoint, switch the line side. This will remove all of the no-load losses of the transformer.
If the low voltage lights used a magnetic dimmer, it was probably dimming the line side of the transformer, which is a magnetic load.
edit: spell check only works if you use it
If the low voltage lights used a magnetic dimmer, it was probably dimming the line side of the transformer, which is a magnetic load.
edit: spell check only works if you use it
jwelectric
Senior Member
- Location
- North Carolina
newt said:
Why are you making this installation to start with?
Occupation: Utility Worker
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
newt,
I think there are several points here.
First. I'm not aware of a readily available listed dimmer, that can operate on a 12 (twelve) V AC source, that can be field installed as part of the Premises Wiring (System) as defined in Article 100.
I'm not saying it doesn't exist, rather, it is probably uncommon and expensive and difficult to install if it does exist.
Second. Is the transformer that powers your low voltage lights a light weight electronic supply, or a heavy magnetic transformer? A magnetic transformer is generally dimmable with a dimmer rated to work with magnetic transformers. As Jeff noted above, they are not cheap.
Third. If the low voltage light power supply is electronic, only the manufacturer of that supply can tell if the supply can be dimmed, and whether a certain type of dimmer is required. Some electronic power supplies are dimmable by standard dimmers, others by "electronic low voltage" dimmers and yet others are not dimmable at all.
I think there are several points here.
First. I'm not aware of a readily available listed dimmer, that can operate on a 12 (twelve) V AC source, that can be field installed as part of the Premises Wiring (System) as defined in Article 100.
I'm not saying it doesn't exist, rather, it is probably uncommon and expensive and difficult to install if it does exist.
Second. Is the transformer that powers your low voltage lights a light weight electronic supply, or a heavy magnetic transformer? A magnetic transformer is generally dimmable with a dimmer rated to work with magnetic transformers. As Jeff noted above, they are not cheap.
Third. If the low voltage light power supply is electronic, only the manufacturer of that supply can tell if the supply can be dimmed, and whether a certain type of dimmer is required. Some electronic power supplies are dimmable by standard dimmers, others by "electronic low voltage" dimmers and yet others are not dimmable at all.
jwelectric
Senior Member
- Location
- North Carolina
newt said:
Then you should know that this dimmer will overload the secondary side of the low voltage transformer.
If you don?t have the installation instructions for the fixture then I suggest that you contact the manufacture with your questions.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Hi Mike.jwelectric said:
I'm not sure what you are getting at here.
jwelectric
Senior Member
- Location
- North Carolina
al hildenbrand said:
This can be approached from two different ways. Either the dimmer will be a resistive dimmer which will increase the work load on the secondary of the transformer of it will be a Solid-state dimmer which will have harmonics that will load the secondary of the transformer.
Although this is a very minimal amount the one time I tried using a dimmer was on low voltage lights lighting the pathway to a hot tub. The transformer gave up after two months. The lights were on no more than 2 hours at one time.
Keep in mind that the transformer is sized for the load of the lights and nothing more.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
I'm still not sure I get your point.
Over the decades, I've installed numerous low voltage lighting systems that I placed on dimmers.
The advent of the solid state lighting transformer is fairly recent, compared to the "decades" of my installations, so most of my dimmed installs were with full wave dimmers (the "expensive" dimmer that Jeff mentions) controlling magnetic transformers.
When the dimmer reduces the energy to the transformer, the voltage is lowered. With a lower voltage on the primary, a proportional lower voltage will arrive at the secondary of the stepdown transformer. With a lower secondary voltage supplying the lamp load, the current flowing in the lamp filaments will be proportionally reduced.
Over the decades, I've installed numerous low voltage lighting systems that I placed on dimmers.
The advent of the solid state lighting transformer is fairly recent, compared to the "decades" of my installations, so most of my dimmed installs were with full wave dimmers (the "expensive" dimmer that Jeff mentions) controlling magnetic transformers.
When the dimmer reduces the energy to the transformer, the voltage is lowered. With a lower voltage on the primary, a proportional lower voltage will arrive at the secondary of the stepdown transformer. With a lower secondary voltage supplying the lamp load, the current flowing in the lamp filaments will be proportionally reduced.
jwelectric
Senior Member
- Location
- North Carolina
al hildenbrand said:
I was talking about installing the dimmer on the low voltage side of the transformer. To use the dimmer on the line side of the transformer is the only way it can be done, that I am aware of.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Out of curiousity, do you recall, was the dimmer you used a simple solid state 120 V dimmer?jwelectric said:
jwelectric
Senior Member
- Location
- North Carolina
It was in the late 70s and I do remember it being a twist knob but don?t remember which type it was. I am guessing that it was a resistive type due to the date.
After the transformer blew I changed the switch to a single pole and switched the transformer on and off instead of the secondary side.
In the mid 90s the house was sold and the lighting was changed to 120 volt lighting and GFCI breaker was installed. The contractor doing that job was my helper during the first installation and he used the original UF cable that was installed.
This is the one and only time that I ever switched the secondary side of a low voltage transformer.
After the transformer blew I changed the switch to a single pole and switched the transformer on and off instead of the secondary side.
In the mid 90s the house was sold and the lighting was changed to 120 volt lighting and GFCI breaker was installed. The contractor doing that job was my helper during the first installation and he used the original UF cable that was installed.
This is the one and only time that I ever switched the secondary side of a low voltage transformer.
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