Quick Q- occupancy sensor in parallel with timer?

[greenspark1]

Hello,
I'm having a pre-senior moment. I'm working on a retail space that needs the lights off most nights, except if someone happens to come in the front door. The visitor is not likely to know where the light switches are. How about putting a simple time clock in parallel with an occupancy sensor near the front door. The hot runs to both TC and OS, then to the load. You then have an either/or situation to light up the night. Any issues here that I'm not thinking of???

 

[Little Bill]

Hello,
I'm having a pre-senior moment. I'm working on a retail space that needs the lights off most nights, except if someone happens to come in the front door. The visitor is not likely to know where the light switches are. How about putting a simple time clock in parallel with an occupancy sensor near the front door. The hot runs to both TC and OS, then to the load. You then have an either/or situation to light up the night. Any issues here that I'm not thinking of???

That's done all the time on outside building or parking lot lights. Except they use a photo cell instead of a occ sensor.
Whether they don't want to change the TC for DST or don't want lights on just because it's cloudy, or other reasons.
It's wired according to what the needs are. Either with the TC ahead of the PC or vise-versa.

Edit: I just realized what I described is wired in series, not parallel. But I still don't see a problem.

 

[greenspark1]

That's done all the time on outside building or parking lot lights. Except they use a photo cell instead of a occ sensor.
Whether they don't want to change the TC for DST or don't want lights on just because it's cloudy, or other reasons.
It's wired according to what the needs are. Either with the TC ahead of the PC or vise-versa.

Edit: I just realized what I described is wired in series, not parallel. But I still don't see a problem.

Thanks for the response. Series definitely isn't an issue and I do it all the time. It's the devices in parallel that is causing little warning bells in my head to trigger. If the TC is off and the OS triggers/closes, any damage or problems putting voltage on both contacts in the TC?

 

[iceworm]

... I'm working on a retail space that needs the lights off most nights, except if someone happens to come in the front door. The visitor is not likely to know where the light switches are. ...

I'm still stuck on this one. The visitor that comes in after hours, and doesn't know where the light switch is - Isn't that called a "burglar". And the act on coming in after hours - Isn't that called Nighttime B&E?

Nothing to do with your question - just curious

ice

 

[GoldDigger]

I'm still stuck on this one. The visitor that comes in after hours, and doesn't know where the light switch is - Isn't that called a "burglar". And the act on coming in after hours - Isn't that called Nighttime B&E?

Nothing to do with your question - just curious

ice

Probably the police or private security responding to the alarm.
They would benefit from having the lights on.

 

[greenspark1]

I'm still stuck on this one. The visitor that comes in after hours, and doesn't know where the light switch is - Isn't that called a "burglar". And the act on coming in after hours - Isn't that called Nighttime B&E?

Nothing to do with your question - just curious

ice

Haha. Yea it is a strange situation. Basically they will have deliveries some nights so the delivery company will have a key but not necessarily the same guy who knows where the light switch is.

 

[greenspark1]

See if this diagram helps explain it.

Any reason this shouldn't work?

 

[GoldDigger]

Does the occupancy sensor require a neutral and do you have that neutral available at the OS location?

 

[iwire]

See if this diagram helps explain it.
View attachment 10770
Any reason this shouldn't work?

It should work fine.

However, in my opinion it violates the rules against small conductors run in parallel.

During the day when the clock contact is closed every time the motion sensor closes you will have small conductors in parallel and none of the exceptions for that fit your situation.

 

[GoldDigger]

1. Since there are intervening devices, I am not convinced that the two paths fall under the parallel conductor restriction.
2. Clearly the "parallel" wiring is not being done with the intention of increasing the carrying capacity of the circuit and both sets of wires are properly OCPD protected. Even if you do not agree with #1, the intent of the restriction is not being violated even if you feel that the letter is.
3. If you put a relay or relays in, does that actually avoid the same quibble? Either the control wires or the relay contacts would still form a parallel circuit in your interpretation.

 

[iwire]

1. Since there are intervening devices, I am not convinced that the two paths fall under the parallel conductor restriction.

As I said, that was my opinion.

The code does not define parallel conductors other than saying they are '(electrically joined at both ends)'.

The conductors are electrically joined at both ends.

2. Clearly the "parallel" wiring is not being done with the intention of increasing the carrying capacity of the circuit and both sets of wires are properly OCPD protected. Even if you do not agree with #1, the intent of the restriction is not being violated even if you feel that the letter is.

That makes no difference at all. If that made a difference there would be no need for exception you reference below. (That exception does not allow paralleling to increase ampacity)

3. If you put a relay or relays in, does that actually avoid the same quibble? Either the control wires or the relay contacts would still form a parallel circuit in your interpretation.

Yes in parallel but then it would fit the exception.

 

[paul]

Check with the installation instructions for your OCC sensor. Most of them do not like to be backfed and it ruins them when you do. You may have to add in a control relay.

 

[greenspark1]

Check with the installation instructions for your OCC sensor. Most of them do not like to be backfed and it ruins them when you do. You may have to add in a control relay.

Thanks for all the responses. Hearing that it may from the OCC is helpful. May switch to a low voltage OCC with a power pack which should alleviate this issue.

 

[kwired]

I'm still stuck on this one. The visitor that comes in after hours, and doesn't know where the light switch is - Isn't that called a "burglar". And the act on coming in after hours - Isn't that called Nighttime B&E?

Nothing to do with your question - just curious

ice

I was wondering the same thing.

Probably the police or private security responding to the alarm.
They would benefit from having the lights on.

I don't call them customers.

Haha. Yea it is a strange situation. Basically they will have deliveries some nights so the delivery company will have a key but not necessarily the same guy who knows where the light switch is.

I guess you cleared up the confusion here.

I see no problem with occupancy sensor that overrides the usual control, or even separate occupancy controlled lighting specifically for this purpose, or if you are utilizing any "night lights" after hours, place them where they are appropriate for the delivery person.

 

[gar]

140817-2345 EDT

Paul:

Neither device is being backfed by a parallel connection. Backfed in this case would require the output voltage to be higher than the input voltage.

There may be some reasons for not paralleling the devices, but this would require a close look at their circuits and how they operate. Logically it is just a non-exclusive or circuit.

.

 

[iwire]

140817-2345 EDT

Paul:

Neither device is being backfed by a parallel connection. Backfed in this case would require the output voltage to be higher than the input voltage.

Gar, to most electricians the above diagram would indicate back-feeding regardless of the voltage levels.

The diagram indicates supplying line voltage to the load side of the device, not all devices like that.

With a standard single pole switch it's not a problem, with electronically controlled occupancy sensors it can kill them.

 

[wirebender]

Why do you need both?
If the lights are on an occ sensor wouldn't they be off anyway?

 

[kwired]

Gar, to most electricians the above diagram would indicate back-feeding regardless of the voltage levels.

The diagram indicates supplying line voltage to the load side of the device, not all devices like that.

With a standard single pole switch it's not a problem, with electronically controlled occupancy sensors it can kill them.

If the ouput of the control device is a dry contact no problem, if the output is solid state devices - be careful it may not like any back-feed of any sort.

 

[GoldDigger]

If the ouput of the control device is a dry contact no problem, if the output is solid state devices - be careful it may not like any back-feed of any sort.

If the occupancy sensor device is, as drawn, a two terminal device, then whether or not the output is via dry contacts the operating power comes from the path through the load or via a ground connection.
In either case, I do not see a difference in practice between the parallel device being closed and the load being open.

 

[kwired]

If the occupancy sensor device is, as drawn, a two terminal device, then whether or not the output is via dry contacts the operating power comes from the path through the load or via a ground connection.
In either case, I do not see a difference in practice between the parallel device being closed and the load being open.

I missed, forgot, etc that there was a drawing posted. If you shunt across that occupancy sensor with the time control - you have no voltage across it - it won't care even if it is a solid state switching device, almost as effective as turning off the supply voltage as far as that occupancy sensor is concerned. JMO. Now if both control devices are two wire devices - no neutral, no dry contacts, they may not like to play well with each other.