Interlocking of 2 Loads from 1 Circuit

[Mr onetwo]

Good morning all, I am installing a new boiler for a friend of mine and I have a question about safety circuit interlocking. In my commercial days the electrician always took care of this, so I have never done the power wiring side of things in this configuration.
There is an existing Polaris water heater that was utilized for both heating and domestic hot water.The heating side never worked properly and wood is used primarily anyway. I am re-piping the system to install a Laars Mini Therm for heating and keeping the Polaris as is for hot water. It is fed by a single 20 amp circuit. Pulling new circuits would be a nightmare and the panel is full.
What would you suggest as the simplest way to interlock the TC1 thermal cutoffs so that when either one trips it kills both appliances? RIB relays or some other way? I have attached a drawing to illustrate. Just not sure of the best way to do this....thanks.

 

[tvand13]

Couple of questions:

Where is this located and what codes are in effect?

What is an "em switch"?

Are these both gas appliances? If they're electric, there's no way they can share a circuit if theyre both running at the same time. Why are they listed as "15A"? Do they need dedicated circuits?

 

[Mr onetwo]

code is NFPA 54
emergency switch
gas...each requires a 15a feed...can be a single circuit so 20 amp is ok.They might draw 5 amps if you are lucky

 

[Innovate1]

Since only one can run at a time due to limitation of feed then one way to do that is make one the primary and power the secondary one only when the first is not running. A little more detail would really help. Why do both units need to be shut off when either cutoff trips? If all you want to do is that you could power a relay from the output of the TC1 and have the NO contacts interrupt the power to the water heater. Then a second relay powered by TC2 with NO contacts supplying the boiler. But it doesn't deal with preventing both on at the same time.

 

[dave*99]

Are the TC1's the ceiling mounted thermal safety cutouts? Like this?


Are you able to make connection s as follows:

Breaker---Emergency switch----TC1(boiler)-----TC1(Water_Heater)---Then go to both service switches.

This puts both TC1 in series and if either opens up, both appliances are disabled.

 

[dave*99]

Since only one can run at a time due to limitation of feed then one way to do that is make one the primary and power the secondary one only when the first is not running. A little more detail would really help. Why do both units need to be shut off when either cutoff trips? If all you want to do is that you could power a relay from the output of the TC1 and have the NO contacts interrupt the power to the water heater. Then a second relay powered by TC2 with NO contacts supplying the boiler. But it doesn't deal with preventing both on at the same time.

As these are gas appliances, this does not seem to be the issue.

 

[PCustoms]

Are the TC1's the ceiling mounted thermal safety cutouts? Like this?


Are you able to make connection s as follows:

Breaker---Emergency switch----TC1(boiler)-----TC1(Water_Heater)---Then go to both service switches.

This puts both TC1 in series and if either opens up, both appliances are disabled.

This was my first thought as well, but I'm not well versed enough in the code to know if that's OK.

 

[BillK]

Are both units sitting next to each other ?? If so why not just use one Thermal switch right above them both ? Split the feed after the Thermal switch. Unless that is not allowed by code.

 

[Mr onetwo]

Are the TC1's the ceiling mounted thermal safety cutouts? Like this?


Are you able to make connection s as follows:

Breaker---Emergency switch----TC1(boiler)-----TC1(Water_Heater)---Then go to both service switches.

This puts both TC1 in series and if either opens up, both appliances are disabled.

That is a TC1...TC2's are square. Your plan makes sense.Why didn't I think of that.

 

[Mr onetwo]

Since only one can run at a time due to limitation of feed then one way to do that is make one the primary and power the secondary one only when the first is not running. A little more detail would really help. Why do both units need to be shut off when either cutoff trips? If all you want to do is that you could power a relay from the output of the TC1 and have the NO contacts interrupt the power to the water heater. Then a second relay powered by TC2 with NO contacts supplying the boiler. But it doesn't deal with preventing both on at the same time.

I'm confused by your answer...I never said only one can run at a time. Code says if there is a problem with appliance #1 that causes a thermal trip then all appliances must shut down if they are in the same space.Doesn't matter if it's 2 or 16 appliances.

 

[Mr onetwo]

Are both units sitting next to each other ?? If so why not just use one Thermal switch right above them both ? Split the feed after the Thermal switch. Unless that is not allowed by code.

The TC1 must be directly over each ignition source as high up as possible.

 

[wyliesdiesels]

Since only one can run at a time due to limitation of feed then one way to do that is make one the primary and power the secondary one only when the first is not running. A little more detail would really help. Why do both units need to be shut off when either cutoff trips? If all you want to do is that you could power a relay from the output of the TC1 and have the NO contacts interrupt the power to the water heater. Then a second relay powered by TC2 with NO contacts supplying the boiler. But it doesn't deal with preventing both on at the same time.

I think you misunderstood his post. He never said both couldnt run at the same time due to the single 20a circuit capacity. Both units running together dont pull more than about 10a so that is inconsequential

what he is trying to do is cut power off to both units in an emergency thermal shutdown caused by one of the units.

 

[Wrench97]

Sounds like the circuit has run through both T1's each mounted above the units then split off to power the 2 units.

 

[wyliesdiesels]

Are the TC1's the ceiling mounted thermal safety cutouts? Like this?


Are you able to make connection s as follows:

Breaker---Emergency switch----TC1(boiler)-----TC1(Water_Heater)---Then go to both service switches.

This puts both TC1 in series and if either opens up, both appliances are disabled.

bingo

TC1s are wired in series.

 

[Mr onetwo]

Thanks guys!