# Intrinsically safe float relay in wet well



## ElectricMatt (Dec 29, 2016)

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## gpop (May 14, 2018)

You should use the intrinsically safe relays for the floats. 

I understand what you are saying about directly connecting to the inputs but this is a industrial standards in waste water so save a argument and add them any way. Seal-off's are also required now so its a good time to upgrade if you haven't already. (use lots of putty and very little cement so you can hit the seals with 2 hammers to remove the float wires when needed)

Im not sure if a methane gas detector is required or recommended. We tend to throw one in on every new panel anyway. (thin line between a new/upgrade and changing out a controller that's are no longer available)


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## varmit (Apr 19, 2009)

You will need intrinsically safe isolators, not relays, on the controls.

You will need to seal the conduit entries for two reasons: 
To avoid a possible explosion from the methane.
To avoid the fumes and gases from corroding everything in the panel.


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## ElectricMatt (Dec 29, 2016)

varmit said:


> You will need intrinsically safe isolators, not relays, on the controls.
> 
> 
> 
> ...




The conduits have sealoffs from electrical room to the junction box for the floats. The conduit from the junction box into the wet well has duct seal in it and is vented as well. 

So even using 24vdc for float controls you are saying I just need to use say a 5 channel isolator(there are 5 floats) in the control panel for the floats? 


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## gpop (May 14, 2018)

ElectricMatt said:


> The conduits have sealoffs from electrical room to the junction box for the floats. The conduit from the junction box into the wet well has duct seal in it and is vented as well.
> 
> So even using 24vdc for float controls you are saying I just need to use say a 5 channel isolator(there are 5 floats) in the control panel for the floats?
> 
> ...


5 floats on a micro controller. 

wouldn't a 4-20ma pressure sensor and 2 floats work as a better level control as you then have a main system using the pressure sensor and a back up system of floats. (if the station has flush valves on the pumps this avoids a lot of problems with tangled floats)

There are a lot of systems on the market that can do both level control with built in isolation.


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## JRaef (Mar 23, 2009)

ISR relays use a highly limited amount of energy in the circuit so as to not be incendiary if something goes wrong. 24VDC may be considered safe from the standpoint of not hurting someone, but without an energy limiting system like a zener barrier it's capable of igniting gasses. In addition, the NEC requires that intrinsically safe circuity be separated away from other non-IS circuits so that there is no possibility of crossed wires putting incendiary energy onto the IS circuits.


Do it right or don't do it...


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## ElectricMatt (Dec 29, 2016)

The 4-20 level sensor was my first thought too. I prefer using analog sensors personally. However waste water is a new area for me and I didn’t know what sensor would work and or survive such a corrosive environment. 

The floats are existing which I why I elected to use them. I am not worried about tangled floats in this particular wet well as they have pretty good separation and a large divider between the clarifier feed pipe and the sludge pumps. 

Why do you say use the relays, it seems like the isolator would be just as compliant and a more cost effective solution? Just looking for explanations from someone who has more experience in this area as I am learning as I go. 

Thank you for the feedback and recommendations 


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## ElectricMatt (Dec 29, 2016)

JRaef said:


> ISR relays use a highly limited amount of energy in the circuit so as to not be incendiary if something goes wrong. 24VDC may be considered safe from the standpoint of not hurting someone, but without an energy limiting system like a zener barrier it's capable of igniting gasses. In addition, the NEC requires that intrinsically safe circuity be separated away from other non-IS circuits so that there is no possibility of crossed wires putting incendiary energy onto the IS circuits.
> 
> 
> Do it right or don't do it...




Great explanation that is what I was looking for! I wondered about the need of a zener barrier(diode), but I have only used those in other class 1 div 1 applications. I am still learning the ins and outs of these systems. Thank you and I am glad to listen to any other recommendations you may have!


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## ElectricMatt (Dec 29, 2016)

gpop said:


> 5 floats on a micro controller.
> 
> 
> 
> ...




Good do you have any particular analog level sensors you recommend for this particular application?


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## splatz (May 23, 2015)

JRaef said:


> In addition, the NEC requires that intrinsically safe circuity be separated away from other non-IS circuits so that there is no possibility of crossed wires putting incendiary energy onto the IS circuits.


The ones I have worked on situate the barrier relay down in the corner of the panel with a sheet metal barrier wall around it, and the float wires come up in a knockout behind the wall.


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## ElectricMatt (Dec 29, 2016)

splatz said:


> The ones I have worked on situate the barrier relay down in the corner of the panel with a sheet metal barrier wall around it, and the float wires come up in a knockout behind the wall.




Splats and Jraef,

Based on what’s splatz said does the NEC require a physical barrier in the control box, or is a zener barrier considered sufficient?



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## gpop (May 14, 2018)

splatz said:


> The ones I have worked on situate the barrier relay down in the corner of the panel with a sheet metal barrier wall around it, and the float wires come up in a knockout behind the wall.


Works better with the 4 gang as the metal fits tighter than 8 pin tube based units.


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## splatz (May 23, 2015)

ElectricMatt said:


> Splats and Jraef,
> Based on what’s splatz said does the NEC require a physical barrier in the control box, or is a zener barrier considered sufficient?


yes 504.30


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## ElectricMatt (Dec 29, 2016)

splatz said:


> yes 504.30




Awesome, thanks you!


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## gpop (May 14, 2018)

ElectricMatt said:


> Why do you say use the relays, it seems like the isolator would be just as compliant and a more cost effective solution? Just looking for explanations from someone who has more experience in this area as I am learning as I go.
> 
> Sent from my iPhone using Tapatalk


We call them relays as they fit in relays bases but the technical term may be a 8 pin tube based isolator. 
From the pictures you have the type that locks to the base. 

I would have to read the manual to see if the lock is considered a type of barrier. 

Most of the ones i use are Diversified Electronics IS024ACE (think that's the number) as they are easy to have a barrier made to fit and they are capable of 4 floats even if we only use 2 on most jobs. (24vac, I think they also make a 120v version)

As for a 4-20ma pressure sensor im not sure of the brand we use its submersible with 40' of cable and 25' of scale. 

If the pressure senor or processor fails then we use a latching relay setup on the high level float to start and run the pumps until the low level unlatch's the pumps. This keeps the station working until we get there to fix it.


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## splatz (May 23, 2015)

this recent post 

https://www.electriciantalk.com/f2/books-help-controls-tech-275856/#post5251386 

links to a pdf of an instrumentation textbook. There is a fair bit of info in there about hazardous locations, look at 32.1. 

After reading it, from a safety perspective, I like the idea of a 4-20ma sensor because when functioning properly it's already at the low energy levels you need for safety, you could say it's already "normally safe" but not safe enough to satisfy the requirements for "intrinsically safe." The barrier is just there for when there's a fault in the field wiring or sensor wiring that could defeat the loop's normal low energy level. 

Floats versus pressure transducer - I prefer the floats, just choose very carefully either way (don't just buy the cheapest thing in stock at Grainger). Consider carefully the maintenance.


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## ElectricMatt (Dec 29, 2016)

splatz said:


> this recent post
> 
> https://www.electriciantalk.com/f2/books-help-controls-tech-275856/#post5251386
> 
> ...




Thank you for the recommendation of that book I am going to get a copy. 

My biggest concern with the pressure transducer was the viscosity of the liquid and possible being able to move that transducer cable giving false readings. 


I like the floats too, probably because that is what is most familiar to me. I buy a good quality one from a local pump supplier we work with. 


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## JRaef (Mar 23, 2009)

You will see that even if you use a pressure transducer, most consultants will require at least one or two floats as safety backups anyway. So you are just discussing how MANY floats you need.


IS _relays _vs zener barriers is really mostly about convenience in the design. Standard relays + IS zener barriers = two sets of things to mount, wire and troubleshoot, ISR = one device. Many of the ISRs have some logic built-in as well.


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## cmdr_suds (Jul 29, 2016)

Even with a 4-20mA transmitter, you will need an IS isolator. 4-20mA by itself is not IS. Make sure the transmitter is suitable for use after an IS isolator. 

Level transmitters are nice in that you can remotely adjust the setpoints in the PLC. Floats have to be manually adjusted (after they are all covered in s...):surprise:
They are also nice if the pumps are on VFDs in that you can throttle the flow to maintain level or at least not surge the process you are pumping into. Gotta keep those bugs happy.:biggrin:


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## FTC (Oct 10, 2016)

4-20 can be intrinsically safe. It's based off power not current. If the max power possible from your device is close to 1w you might be okay. Of course, it still needs to certified but you should be able to find some. Is this a closed vessel? Do you have clean instrument air on-site?


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## paulengr (Oct 8, 2017)

A lot of the loop powered 4-20 mA stuff is IS already, just need the barrier. Second a lot of it has one auxiliary relay output. I didn’t spot one out right but it’s a common feature. Most of the wastewater plants I’ve worked with have either a bubbler (pressure transmitter) or an ultrasonic level sensor and a backup high level float only. Contrary to what some consultant thinks, floats at least in sewage are notorious for getting either buried in debris where they fail or hung up somewhere or something. Even the “float in a stick” kind. So I’m not seeing high reliability compared to a sensor that sits above the well and never comes in contact, which is why most of them prefer level transmitters. Plus if you have RTU data you can see when it fails because no matter what it does the signal either flat lines or becomes pure noise when it’s broke. The remaining float usually doesn’t even work because it gets used so little.


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## paulengr (Oct 8, 2017)

FTC said:


> 4-20 can be intrinsically safe. It's based off power not current. If the max power possible from your device is close to 1w you might be okay. Of course, it still needs to certified but you should be able to find some. Is this a closed vessel? Do you have clean instrument air on-site?



Flowline sells several certified IS models among others. The loop powered units run under 0.1 W. So with around 14 VDC worst case past the.barrier and 4 mA max current that’s around 0.05 W. Not much power but they exist and work. The only remaining thing special to meet the technical requirement of IS is not to store energy (charge a big capacitor) which level sensors don’t need anyway. Depending on how it’s mounted (high enough) often the installations I’ve seen are non hazardous locations anyway.


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## paulengr (Oct 8, 2017)

“Clean air” for bubblers which is definitely a non hazardous location method is normally two small aquarium bubbler pumps piped together (redundancy). Never know what you will get on plant air.


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## gpop (May 14, 2018)

We always use 2 floats no matter what the sensor is. 

High high float latches a relay and parallels what ever is being used for auto. Low level unlatches the relay.

If everything works ok then the low level will stay under water in the closed position and the high level will never get wet.
Recently we have been playing with a precision digital pd 6000-6r4 as a cheap controller. Its a basic 4-20ma in 4 relay out controller that also does loop power, alternation and pump delay (useful if you have generator back up).


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## ElectricMatt (Dec 29, 2016)

gpop said:


> We always use 2 floats no matter what the sensor is.
> 
> High high float latches a relay and parallels what ever is being used for auto. Low level unlatches the relay.
> 
> ...




This one actually does have a backup generator, but it already has a timing relay panel for the whole facility. 

As far as the five floats, it is by request. In the following order from bottom to top:
1 - low level lockout
2 - pumps off
3 - pump call
4 - call lag pump
5 - high level alarm( this is for their remote monitoring system) 

I did find a level transmitter(radar) that would work for this application. I am not going to put it in this particular wet well, but will be considering it in the future. (With backup floats of course). 


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## ElectricMatt (Dec 29, 2016)

gpop said:


> We always use 2 floats no matter what the sensor is.
> 
> High high float latches a relay and parallels what ever is being used for auto. Low level unlatches the relay.
> 
> ...




I meant to comment on the controller. I like using the micro820 controllers. They are incredibly cost effective, I already have the basic program built for most applications, and I can attach HMI’s or other communication items via the built in Ethernet port. I can buy them for about the same as a 3 way alternating relay, and have no need for additional timers, or fail safe relays in the system. Basically it allows me to bring down the cost and complexity of the system. 


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## gpop (May 14, 2018)

ElectricMatt said:


> I meant to comment on the controller. I like using the micro820 controllers. They are incredibly cost effective, I already have the basic program built for most applications, and I can attach HMI’s or other communication items via the built in Ethernet port. I can buy them for about the same as a 3 way alternating relay, and have no need for additional timers, or fail safe relays in the system. Basically it allows me to bring down the cost and complexity of the system.
> 
> 
> Sent from my iPhone using Tapatalk


Im all for automation. On most of the stations we have control logixs and touch screen hmi's but you have to ask if this is a good or bad thing.

1/ In the event of a failure who is capable of fixing the problem
2/ How long will it take the person to get there
3/ does it require special software
4/ does it require a licence
5/ Is there internet access to download required software
6/ whats plan B if person is unavailable (back-ups)
7/ Can a contractor fix the problem walking in blind
8/ if a part like a vfd is unavailable can a different brand be used
9/ whats the lead time on parts

How long before it goes from a electrical problem to a major problem/shutdown.


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## ElectricMatt (Dec 29, 2016)

gpop said:


> Im all for automation. On most of the stations we have control logixs and touch screen hmi's but you have to ask if this is a good or bad thing.
> 
> 
> 
> ...




So I couldn’t agree more, but there is some limitation to the ‘what if’ scenario. If I use a 3 way alternating relay what is the odds anyone will have one in stock? Slim to none. 

All the plants I put these in is a client of the company I work for, so it will be me or one of my guys fixing it late at night. 

As for response time, I have an average of 1 hour response, the company as a whole is a little over an hour. 

As for the rest. I always try to sell an extra prime programmed controller with the system. However, on benefit of the micro820 is the sad slot. I always leave an SD card with the program loaded on it along with a detailed set of drawings of wiring and basic operation of the system. 

That SD cars can be loaded into any other micro 820, and as soon as it boots will load the program onto the controller. 

These controllers I typically have no more than a 1 day lead time on. 

These are great considerations, and things I definitely try to take into account when I am designing/installing. Mostly because I have been that guy too many times walking into a poorly and over designed system, that I have had to redo with what I could access just to get the customer running. 

If your contractor cannot find a way to get you running, temporarily, then you are using the wrong contractor. There is nothing I can do if a client has a poor choice in a controls contractor. 

I love the devils advocate approach, that is my favorite role to play. 


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## ElectricMatt (Dec 29, 2016)

GPop,

Please don’t take my response as I think I know everything. 

I still have a ton to learn, which is why I come here. I read and ask questions to all of you out there who are more experienced in particular areas than I am. 

I am always amazed with the response, and thought that goes into them. I am very appreciative of everyone who responds and how quickly they do it. Also, I am very grateful to everyone. It is the information given that helps me to continue to excel in our field. 


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## gpop (May 14, 2018)

ElectricMatt said:


> GPop,
> 
> Please don’t take my response as I think I know everything.
> 
> ...



I don't take offence. I actually think your response is valid.

1 hr call in, SD card load, more than one person available and a spare available some where local.


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## kyles (6 mo ago)

gpop said:


> We call them relays as they fit in relays bases but the technical term may be a 8 pin tube based isolator. From the pictures you have the type that locks to the base. I would have to read the manual to see if the lock is considered a type of barrier. Most of the ones i use are Diversified Electronics IS024ACE (think that's the number) as they are easy to have a barrier made to fit and they are capable of 4 floats even if we only use 2 on most jobs. (24vac, I think they also make a 120v version) As for a 4-20ma pressure sensor im not sure of the brand we use its submersible with 40' of cable and 25' of scale. If the pressure senor or processor fails then we use a latching relay setup on the high level float to start and run the pumps until the low level unlatch's the pumps. This keeps the station working until we get there to fix it.


 Level rat or KPSI with a specific PSI range deep enough for wetwell. They are 2 wire looped power system. Makes installing a barrier on them easy.


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## oldsparky52 (Feb 25, 2020)

OOPS!


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