# RTU's(roof top units)



## CFine (May 20, 2008)

OK, I know i have to Pipe each unit to the panel in the machine room/rooms. What else should I be Looking at? Foreman put me on RTU's and i've never done them before i'm usually Service or Lighting. Any Help would be appreciated. I mainly need to know if i have to provide a 2nd conduit for control wiring and if so do i penetrate the roof right by the unit. Just need an idea what i should be looking at. any help would be appreciated. Thanks.


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## Bob Badger (Apr 19, 2009)

It depends on the unit but usually I come up inside the curb with the power control and fire alarm system wiring without penetrating the roof itself.


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## CFine (May 20, 2008)

So i Run my conduit like normal for Power and i'll Run a 2nd Conduit for the control and fire alarm to the curb and i can plastic bushing the conduit and i should be fine as long as i label it?


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## Magnettica (Jan 23, 2007)

Bob Badger said:


> It depends on the unit but usually I come up inside the curb with the power control and fire alarm system wiring without penetrating the roof itself.


Fire alarm system wiring? 

What do you attach that to in the RTU?


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## Magnettica (Jan 23, 2007)

CFine, you're also going to need a GFCI-protected receptacle within 25' of each RTU.

NEC 210.63


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## CFine (May 20, 2008)

Magnettica said:


> Fire alarm system wiring?
> 
> What do you attach that to in the RTU?


The print shows Smoke detectors in the ducts.


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## Magnettica (Jan 23, 2007)

CFine said:


> The print shows Smoke detectors in the ducts. What about the GFCI how many would i need and why? sorry first time doing RTU's


In the ducts, ok. I'm not much of a commercial guy so that's why I asked.

The number of receptacles on the roof would depend on the size of the roof and the number of RTU's too.


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## CFine (May 20, 2008)

ok so spread out over the Roof of the building, each unit will have to have at least 1 conduit of the correct size Going to the panel, plus a GFI and then a Conduit for the control wire. for the Power Do i penetrate the Roof or do i use the Curbs? running 1 1/2 inch to 2 inch conduit is gonna be tough to get through those.


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## Bob Badger (Apr 19, 2009)

Magnettica said:


> Fire alarm system wiring?
> 
> What do you attach that to in the RTU?


Typically duct smoke detectors and unit shut down connections.


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## CFine (May 20, 2008)

Magnettica said:


> In the ducts, ok. I'm not much of a commercial guy so that's why I asked.
> 
> The number of receptacles on the roof would depend on the size of the roof and the number of RTU's too.



Yea i'm usually doing Lighting or the service on the building i was prepared to do lighting like normal and they hit me with RTU's. but i like to learn new things and this is something i need to learn and should know.


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## B4T (Feb 10, 2009)

Magnettica said:


> Fire alarm system wiring?
> 
> What do you attach that to in the RTU?


The FACP has to shut down the blower motors if they are part of RTU


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## wildleg (Apr 12, 2009)

you should probably check the plans and check with your foreman on the installation you plan on doing. 

- you can run inside the curbs on most modern package units. sometimes you pipe to a box under the roof and flex up, sometimes you pipe all the way, sometimes you run mc all the way. sometimes you run pipe thru the roof and branch to the units. modern package units usually have the disconnects built into them now, and some have gfi receptacles built into them also. sometimes you gotta put lots of discos on the roof. you need a plan and cut sheets on the units (or the units in place) to know what you are doing.


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## Magnettica (Jan 23, 2007)

Bob Badger said:


> Typically duct smoke detectors and unit shut down connections.


Similar to that of an ansul system to shut out fresh air that feeds a fire?


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## CFine (May 20, 2008)

wildleg said:


> you should probably check the plans and check with your foreman on the installation you plan on doing.
> 
> - you can run inside the curbs on most modern package units. sometimes you pipe to a box under the roof and flex up, sometimes you pipe all the way, sometimes you run mc all the way. sometimes you run pipe thru the roof and branch to the units. modern package units usually have the disconnects built into them now, and some have gfi receptacles built into them also. sometimes you gotta put lots of discos on the roof. you need a plan and cut sheets on the units (or the units in place) to know what you are doing.


I'm going to have to do that to see how the piping has to be Run, Have to have J box for the control. GFCI's aren't on the Unit but the disconnect are. I'm Hoping i can get away with piping it on the Roof, the floor has so many Stub ups and Crap that i got no Room for a Lift at all.


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## jwjrw (Jan 14, 2010)

Magnettica said:


> Similar to that of an ansul system to shut out fresh air that feeds a fire?


Yep similar to that. You want the ventilation shut down if the building is on fire.


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## B4T (Feb 10, 2009)

Even with central A/C units in homes, the 120V smoke detector shuts down the blower unit to keep the unit from spreading smoke through out the house.


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## jwjrw (Jan 14, 2010)

Black4Truck said:


> Even with central A/C units in homes, the 120V smoke detector shuts down the blower unit to keep the unit from spreading smoke through out the house.


 
Ive never seen a duct detector in a resi app here. I'm sure they are out there but I've never seen one.


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## CFine (May 20, 2008)

jwjrw said:


> Ive never seen a duct detector in a resi app here. I'm sure they are out there but I've never seen one.


the only place i've seen them is in condo/apartment style resi, but never in houses.


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## B4T (Feb 10, 2009)

jwjrw said:


> Ive never seen a duct detector in a resi app here. I'm sure they are out there but I've never seen one.


Not a duct detector, they install a line voltage unit in the hallway that shuts down the blower unit.

Most air returns are located in this area


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## jwjrw (Jan 14, 2010)

Black4Truck said:


> Not a duct detector, they install a line voltage unit in the hallway that shuts down the blower unit.
> 
> Most air returns are located in this area


 
Never seen them do that here. Is it a code requirement where you are?


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## B4T (Feb 10, 2009)

jwjrw said:


> Never seen them do that here. Is it a code requirement where you are?


Yes, might be building code


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## william1978 (Sep 21, 2008)

jwjrw said:


> Ive never seen a duct detector in a resi app here. I'm sure they are out there but I've never seen one.


 I haven't seen them either.


CFine said:


> the only place i've seen them is in condo/apartment style resi, but never in houses.


 I haven't seen them there either. That must be a local thing for your area.


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## Magnettica (Jan 23, 2007)

We never tie in the 120 smoke detectors with any part of the HVAC system, never. 

The difference here is likely the words "detectors" and "alarms".


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## CFine (May 20, 2008)

william1978 said:


> I haven't seen them either.
> 
> I haven't seen them there either. That must be a local thing for your area.


No, it was a addition by the Building owner he wanted it so they had to be added in.


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## william1978 (Sep 21, 2008)

CFine said:


> No, it was a addition by the Building owner he wanted it so they had to be added in.


 Ok, I got you.:thumbsup:


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## william1978 (Sep 21, 2008)

Magnettica said:


> CFine, you're also going to need a GFCI-protected receptacle within 25' of each RTU.
> 
> NEC 210.63


 A lot of the new RTU's that I have seen have come with the rec built in from the factory.


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## randomkiller (Sep 28, 2007)

First off it all depends on the job specs, often we don't have anything to do with control or FA wiring. Whats in the contract? We never use a roof penetration for wiring, we go inside the curb only. You will need a service outlet and light per AHJ specs. Most FA fan kill circuits are wired with plenum rated wire pulled into the unit through a factory installed bushing or provided ko. Aaon units normally have the service outlet factory installed, as do some larger Trane units.


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## randomkiller (Sep 28, 2007)

jwjrw said:


> Never seen them do that here. Is it a code requirement where you are?


 
Normally larger jobs have a fan kill circuit in the FA panel in addition to duct smoke detectors installed in the units.


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## randomkiller (Sep 28, 2007)

jwjrw said:


> Ive never seen a duct detector in a resi app here. I'm sure they are out there but I've never seen one.


To the best of my knowledge any airhandling unit with an output of 2000cfm or more needs a duct mounted smoke detector. Most resi isn't that large. Over 4000cfm one is required in both supply and return ducts.


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## user4818 (Jan 15, 2009)

Black4Truck said:


> Yes, might be building code


Have you actually seen this code requirement or is it just done by tradition? 

We have a similar local fire alarm code requirement but it's only for furnaces or RTU's over a certain CFM rating which escapes me at the moment.


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## randomkiller (Sep 28, 2007)

Peter D said:


> Have you actually seen this code requirement or is it just done by tradition?
> 
> We have a similar local fire alarm code requirement but it's only for furnaces or RTU's over a certain CFM rating which escapes me at the moment.


 
could it be 2000cfm?


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## user4818 (Jan 15, 2009)

randomkiller said:


> could it be 2000cfm?


Yup, that's it. :thumbsup: I just looked it up.

Our local code also requires 4 or more ceiling fans in the same room to be shut down as well.




> (Add) 13.8.10.5.10
> 
> In all buildings having a fire alarm system, the fire alarm system shall be interconnected to the
> building's heating, ventilation and air conditioning [HVAC] line voltage controls so that the
> ...


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## miller_elex (Jan 25, 2008)

Check to see if the disconnect is integral with the unit. 

Also check to see if the control panel is on the roof or inside the building.


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## 480sparky (Sep 20, 2007)

Magnettica said:


> We never tie in the 120 smoke detectors with any part of the HVAC system, never.
> 
> The difference here is likely the words "detectors" and "alarms".


I have installed relays that will open the low-voltage power that controls resi HVAC. Smokes go off, furnace & air shut down.

It's quick, easy, and a great profit-maker.


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## B4T (Feb 10, 2009)

Peter D said:


> Have you actually seen this code requirement or is it just done by tradition?


No.. it wasn't by "tradition" :laughing:

I personally have not got involved with it, but I have seen a few jobs where the A/C guys put the smoke in that killed the blower unit.

They have a restricted use license and that allows them to do this, according to them, of course


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## jwjrw (Jan 14, 2010)

william1978 said:


> I haven't seen them either.
> 
> I haven't seen them there either. That must be a local thing for your area.


 
We did a 5 story condo on Queens Rd. I know the penthouse had duct detectors in it but only because of its size im sure.


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## jwjrw (Jan 14, 2010)

randomkiller said:


> To the best of my knowledge any airhandling unit with an output of 2000cfm or more needs a duct mounted smoke detector. Most resi isn't that large. Over 4000cfm one is required in both supply and return ducts.


 
Yep and when you said that I remembered a large condo I did that had them in it.


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## CFine (May 20, 2008)

Well this is what we decided to do, Pipe Power On top of the Roof, Control and FA on the inside underneath.


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## randomkiller (Sep 28, 2007)

CFine said:


> Well this is what we decided to do, Pipe Power On top of the Roof, Control and FA on the inside underneath.


 
What kind of units are they?


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## B4T (Feb 10, 2009)

CFine said:


> Well this is what we decided to do, Pipe Power On top of the Roof, Control and FA on the inside underneath.


Didn't the A/C guys use a "pitch pocket" for their refrigerant lines?

I always give them (2) pieces of flex PVC to run before foam and tar.


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## Bob Badger (Apr 19, 2009)

Black4Truck said:


> Didn't the A/C guys use a "pitch pocket" for their refrigerant lines?


I think we are talking commercial self contained RTUs, there would be no pitch pockets.




CFine said:


> Well this is what we decided to do, Pipe Power On top of the Roof,


Did anyone look at the job specs and make sure that is acceptable?

For instance if you go up on a Lowe's roof the only thing you will see is gas lines and RTUs, not a bit of conduit exposed.


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## cobra50 (Aug 12, 2009)

I remember that anything 3 tons and under did not require a local duct detector on the supply side. You just break the "G" leg with the N/C contact. If there was FA in the building we ran the loop thru the initiation contacts N/O. I think we ran a 14/4 FA for power and fan shutdown reset from FA panel.


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## CFine (May 20, 2008)

Yea we check the job specs, and waited all day for a confirmation and got it.


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## william1978 (Sep 21, 2008)

jwjrw said:


> We did a 5 story condo on Queens Rd. I know the penthouse had duct detectors in it but only because of its size im sure.


 Well Queens Rd really narrows it down.:laughing::laughing::laughing:


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## Voltech (Nov 30, 2009)

I would make sure your supposed to make the penetration. I have seen that done on some jobs and the roof wont warranty the roof. Sometimes the roofer or HVAC guys make a chase for your raceway and his lines.

Of course this only matters if the roof is already on.


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## randomkiller (Sep 28, 2007)

Black4Truck said:


> Didn't the A/C guys use a "pitch pocket" for their refrigerant lines?
> 
> I always give them (2) pieces of flex PVC to run before foam and tar.


 
A condenser will have refrigerent lines not a RTU.


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## randomkiller (Sep 28, 2007)

cobra50 said:


> I remember that anything 3 tons and under did not require a local duct detector on the supply side. You just break the "G" leg with the N/C contact. If there was FA in the building we ran the loop thru the initiation contacts N/O. I think we ran a 14/4 FA for power and fan shutdown reset from FA panel.


 
5tons (2000 cfm) is the breaking point, breaking the "G" terminal doesn't always give instant shut down, breaking the hot (R) side of the 24v trans
will take out the fan even with a time delay relay.


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## Bob Badger (Apr 19, 2009)

We can forget 'tons' it is just the CFM, if you have a heating only unit that moves more than 2000 CFM you will need to rig it for shutdown if it was not already provided with a factory installed smoke detector.

All buildings are different so there are many ways to accomplish shut downs, I prefer to break the transformer output as Random killer mentioned if the prints do not specify.

Some times you do not want to kill the control power, sometimes the RTUs are part of the smoke evacuation and pressurization systems.

I have down some large 'Anchor stores' at malls and the the store fire alarm system would control the RTUs and smoke evac. fans. If smoke was detected in the store the RTUs would shut down close the fresh air dampers and start the smoke exhaust fans. This would keep the smoke from going out into the mall.

On the other hand I also installed smoke detectors in the mall space and if these detectors sensed smoke in the mall all the RTUs would switch to full fan and the fresh air intakes would open fully, the smoke exhaust fans would stay off.

This would pressurize the store and keep the smoke out in the mall.

At one store as part of commissioning we had to test these systems using a smoke generator that was rented from a stage rental company. The systems worked very well.


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## CFine (May 20, 2008)

So our RTU's Arrived today, i got all 11 of them piped ready to go. but we got no crane to put them on the roof. lol.


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## jwjrw (Jan 14, 2010)

william1978 said:


> Well Queens Rd really narrows it down.:laughing::laughing::laughing:


 
Hmmm queens rd west I think. It was 611 or 6 something. Right near the hospital. Tim Walker was my inspector.


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## william1978 (Sep 21, 2008)

jwjrw said:


> Hmmm queens rd west I think. It was 611 or 6 something. Right near the hospital. Tim Walker was my inspector.


 That must have been atleast 2 years ago. He has been retired that long.


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## JohnR (Apr 12, 2010)

I connected a D-smoke to the FA panel onetime which was pre-wired from the factory, my foreman at the time didn't want a separate 24V power run to feed them from the FACP so we left them powered from the unit itself. well somehow the hvac guys had the thermostat wired backwards.

This was in November and it was pumping out pure unadulterated A/C so the fellow working under this one unit would shut off the disco for it, which gave a trouble to the FACP . We kept having to go out to the site and turn back on the unit and silence the trouble . 

BTW the outlet built in the unit won't count as the required service 25' outlet if it is wired from the unit main feed after the disco. learned that the hard way once.


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## mattsilkwood (Sep 21, 2008)

CFine said:


> So our RTU's Arrived today, i got all 11 of them piped ready to go. but we got no crane to put them on the roof. lol.


 Thats seems odd. I don't think I've ever been on a job where the tinners didn't set the RTUs. 
A lot of them anymore will use a helicopter and fly them in. I've seen that countless times but I'm still like a little kid every time.


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## jwjrw (Jan 14, 2010)

william1978 said:


> That must have been atleast 2 years ago. He has been retired that long.


I want to say it was 2008 but could of been 2007. Travis M was with him doing training. I don't think he had been an inspector long. I guess it could of been 2006. Time flys by so fast and the jobs all merge together in my mind.


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