Can RCCB trigger falsely when it is in line with induction motors?

[Wrichik Basu]

We have a sanctioned load of 63 A from the electricity supply company (AC RMS 230 V in my country). We have, however, not yet been able to upgrade our 45 A main fuse. Due to this constraint, we cannot run more than one high-current-drawing appliance simultaneously, like two air conditioners or one AC and one microwave. We are planning to upgrade the fuse and install a 63 A DP MCB.

I want to also install a 63 A DP RCCB after the MCB for better protection. Preferably one with ΔI = 30 mA. But I think I read somewhere (can't find it at the moment) that RCCBs may trip falsely when induction motors like air conditioner compressors are in series with it. It was written that induction motors draw a large current when they start, which can be detected by an RCCB as an imbalance between the live and neutral currents, thereby making it trip. Is this true?

 

[Averagesupernova]

That's not really possible to answer accurately. A safe installation of an appliance should never have an actual imbalance of currents in the conductors. But I cannot reliably say that the RCCB device used is not going to give false trips due to a poor design, etc.

 

[Wrichik Basu]

That's not really possible to answer accurately. A safe installation of an appliance should never have an actual imbalance of currents in the conductors. But I cannot reliably say that the RCCB device used is not going to give false trips due to a poor design, etc.

So in an ideal scenario, it shouldn't trip, right?

 

[Wrichik Basu]

There are three other options that I can think of in case it's common (but not ideal) for induction motor loads to falsely trip off RCCBs:

1. Install a 40A RCCB and connect the common house wiring through it, bypass big loads like air conditioners directly to the MCB. The RCCB would still see induction loads like vacuum cleaners or washing machines, though.
2. Install a 63A DP changeover switch. One set of inputs will be powered directly from the MCB, and another set from MCB → RCCB. In case the RCCB starts tripping falsely, the changeover would allow a temporary solution.
3. Scrap off the idea of using a RCCB.

 

[Averagesupernova]

I'm the USA we use GFCI devices. Ground Fault Circuit Interrupters. They do the same thing as what you intend to accomplish. However, they do not protect the entire installation with one device. Unfinished areas need to be protected such as garages, basements with nothing on the floor except concrete, and of course outdoor outlets.
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Individual circuit breakers can contain GFCI protection, more commonly the outlet that appliances are plugged into contain this protection. They can be wired so everything downstream is also protected. Do you not have such devices in your country?

 

[berkeman]

Individual circuit breakers can contain GFCI protection, more commonly the outlet that appliances are plugged into contain this protection. They can be wired so everything downstream is also protected. Do you not have such devices in your country?

Agreed, I've never heard of a giant GFCI on a whole-house distribution breaker. That seems pretty problematic...

 

[Averagesupernova]

Agreed, I've never heard of a giant GFCI on a whole-house distribution breaker. That seems pretty problematic...

It certainly does. I've read about electrical systems in other countries and several times it's been implied that this is the case. I always assume I misunderstand but it always comes back to the same implication. Maybe I'm just not too smart?

 

[berkeman]

Agreed, I've never heard of a giant GFCI on a whole-house distribution breaker. That seems pretty problematic...

I've read about electrical systems in other countries and several times it's been implied that this is the case.

In addition to all the false-trip implications, should a simple trip in the kitchen kill power to the whole house and power off all the people working from home? Not good...

 

[Wrichik Basu]

Do you not have such devices in your country?

I've never heard of a giant GFCI on a whole-house distribution breaker.

I've read about electrical systems in other countries and several times it's been implied that this is the case. I always assume I misunderstand but it always comes back to the same implication.

Let me clear things up a bit. We don't have GFCI outlets in India. Instead, we have to install one for the entire house. These RCCBs are costly; their prices rise with rating, similar to a diode characteristics graph in the first quadrant. That's why most people don't even bother installing one; it's not even available locally, and I have to buy from Amazon. If you have money, no one is stopping you from installing low-rated RCCBs for small sections of your house, though.

Found one writing on RCD nuisance tripping; that discourages me quite a lot from pursuing this plan.

 

[Rive]

You had that horrific adventure with that thin 'protective earth' wire, right?
After such experiences I would rather take that 'nuisance' as 'warning' instead.
Even in your example story there was something fishy found at the end.

As general idea, I would also support the idea of segments instead of a single block.
If you can't or don't want to do it in one go you can still leave appropriate place on the switchboard for later addition.

 

[Wrichik Basu]

You had that horrific adventure with that thin 'protective earth' wire, right?

Yes, unfortunately.

After such experiences I would rather take that 'nuisance' as 'warning' instead.
Even in your example story there was something fishy found at the end.

So, if I get it right, you are saying that given the state of the wiring in my house, I may face a lot of nuisance tripping. Am I correct?

As general idea, I would also support the idea of segments instead of a single block.
If you can't or don't want to do it in one go you can still leave appropriate place on the switchboard for later addition.

This is how the wiring is done in our house at the moment:

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And this is the design I want to implement:

The only purpose of the changeover switch is to make sure that if the RCCB trips falsely, power can be restored without spending a night in the darkness. Of course, passing even the large appliances though a higher rated MCB is what I wanted initially, but that may actually not be possible in the end.

We also have frequent voltage fluctuations, mostly sudden decrease by 20-30 V. Can these too trip the RCCB falsely?

 

[Rive]

So, if I get it right, you are saying that given the state of the wiring in my house, I may face a lot of nuisance tripping. Am I correct?

Not exactly. What I'm trying to say is, that based on what I know about the state of that wiring I would not consider any tripping as 'nuisance'.

The only purpose of the changeover switch is to make sure that if the RCCB trips falsely, power can be restored without spending a night in the darkness.

I think a safety measure cannot be considered safe if it can be bypassed by a simple switch.

I would rather consider having the sufficiently insulated parts of the wiring (for example: permanently installed lights) in a separate segment, off the RCCB.

We also have frequent voltage fluctuations, mostly sudden decrease by 20-30 V. Can these too trip the RCCB falsely?

I think they should not be able to.

 

[DaveE]

We also have frequent voltage fluctuations, mostly sudden decrease by 20-30 V. Can these too trip the RCCB falsely?

Yes, maybe.

PS: The problem with disturbances on the distribution lines is there there are many potential causes and results, so they just aren't very predictable. Transients can couple capacitively into the ground net, which can look like a local ground fault. Normal operation is 50/60Hz, but disturbances have higher frequency components.

 

[tech99]

In the UK we now have types A, AC and B RCCDs for differing applications. For instance, some RCCDs might not like a small DC component in the circuit, filter capacitors on the load, or double-pole switching. It is possible your induction motor has unbalanced capacitance to ground during starting. I think it is an area for professional advice.

 

[DaveE]

I think this is a case for finding local experts that are familiar with your local conditions, regulations, and available devices. I know that mains power distribution & quality is quite different here in Silicon Valley than in rural Texas. I have no idea about India. Book learning only goes so far.

 

[Averagesupernova]

Based on some trouble I recall the OP having in the past it seems it's difficult to obtain the so-called 'local experts'.
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Rather than a changeover switch would it be possible to have several separate RCCD protective devices? One device tripping will not darken the whole house.

 

[Wrichik Basu]

I would rather consider having the sufficiently insulated parts of the wiring (for example: permanently installed lights) in a separate segment, off the RCCB.

Good idea. For that, I will have to install an RCCB inside the house and do some rewiring. Doable. I will think about it.

In the UK we now have types A, AC and B RCCDs for differing applications.

Should've mentioned, I am aiming for a type AC RCCB.

I think this is a case for finding local experts that are familiar with your local conditions, regulations, and available devices.

I think it is an area for professional advice.

I am sick and tired of the "local experts", believe me. I spoke to two stores and an electrician before posting here, they told me why waste money when most people are just happy with an MCB? I asked them what will happen if someone gets in touch with the live wire. They said the MCB will trip anyway when too much current flows though the body. "Yeah, sure," I said and left.

Rather than a changeover switch would it be possible to have several separate RCCD protective devices? One device tripping will not darken the whole house.

Theoretically, yes, it would be possible to do that. That is indeed what should be done. But, that would increase the costs quite a bit. I will keep it in mind.

 

[Averagesupernova]

In the USA a GFCI trips at 5 mA. The specs you are talking about helps prevent fires but is too much current to protect against shock. My 2¢.

 

[Wrichik Basu]

I believe I can at least check for ground faults before installing the RCCB by switching off the DP main fuse downstairs. That will disconnect the neutral and ground, and testing continuity with a multimeter should give an open circuit.

 

[Wrichik Basu]

In the USA a GFCI trips at 5 mA. The specs you are talking about helps prevent fires but is too much current to protect against shock. My 2¢.

Well, something is better than nothing, I guess. Getting electrocuted at 30 mA is perhaps slightly better than getting grilled at short circuit current.

 

[Rive]

Theoretically, yes, it would be possible to do that. That is indeed what should be done. But, that would increase the costs quite a bit.

You need a lot smaller (lower current) device for known low loads like lights, compared to outlets, for example.
Also, you can have them installed later if you prepare the space for them.

I would do that (prepare the space and have them only later on) for the other non-protected devices too, by the way. In-house everyday appliances are the most important, but the rest should not be abandoned either.

 

[Wrichik Basu]

You need a lot smaller (lower current) device for known low loads like lights, compared to outlets, for example.
Also, you can have them installed later if you prepare the space for them.

I would do that (prepare the space and have them only later on) for the other non-protected devices too, by the way. In-house everyday appliances are the most important, but the rest should not be abandoned either.

Upon further thought, it appears that separating the low current devices and the outlets will actually require a lot of rewiring. In the switch boxes in each room, the outlets are attached to the lights in parallel within the switch box itself, so we would have to draw long wires from the fuse box to isolate the outlets. Now, last time we wanted to add an outlet at a different place for our convenience, the electrician found that many of the conduits within the wall were mistakenly cemented when the house was built. Therefore, in many places, we would have to draw external wires. That's going to be one hell of a job. We will keep space in the main fuse box inside the house, but for now, I need to think of a plan that allows me to install an RCCB.

 

[Guineafowl]

This advice from the UK, where, generally speaking, 30mA earth leakage protection is required on all socket and lighting circuits. We’ve had these for a long time, and 30mA is the level required for fire and shock protection.

I’ll use the term RCD, equivalent to RCCB.

Best practice is to have an RCD per circuit, rather than one RCD monitoring many circuits. This is to prevent cumulative tripping from multiple small earth leakage sources, from normal operation eg interference suppression.

To answer your question, a motor surge current should NOT trip the RCD. If this happens, the motor and its circuit should be investigated before blaming the RCD itself. RCDs over here are tested periodically for trip level and trip time under various conditions.

Depending on the results of the tests, you can either up-rate the RCD to 100mA, or change to an S-type time delay unit. Both changes will negate shock protection, but not fire. You could then fit a standard 30mA unit closer to the motor. This would help if an unusually long cable run, and its reactive coupling, is responsible for the tripping, but retain shock protection at the appliance end.

 

[Rive]

going to be one hell of a job.

Ugh.
Indeed.
Try to keep the foundations of a future re-wiring in mind, otherwise it'll be just another patching in the decades long line what led to the present state.

 

[Wrichik Basu]

After some further thoughts, I think I have two plans to replace the 63 A RCCB with:

1. Two 40A RCCBs — one for the lights, and one for all the heavy load appliances.
2. Two 25 A and one 40 A RCCB — two 25A ones for the low loads, and one 40 A for all the heavy loads.

#1 will be less costly, but #2 is preferable in theory because the whole house won't become dark due to a single tripping.

 

[Averagesupernova]

I'm not sure about details where you are at. I am certainly not familiar with conventions outside North America. But is it possible to split things up so when the RCCB trips it doesn't leave your entire house in the dark?
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Edit: As I look closer I see you do in fact have the right idea. My bad.

 

[Guineafowl]

I’d go with option 2, on the principle that the more compartmentalised the setup, the less chance there is of a fault on one circuit affecting another. It’s also much easier to fault-find that way. I would put lights on their own RCD, since being plunged into darkness due to a fault unrelated to lighting is far from ideal.

Are RCBOs available where you are? These are combined RCD and MCB devices, covering earth leakage, overload and short circuit faults. They fit directly in place of the old breaker, and cover just that circuit.

As an aside, in years gone by, UK homes were covered by two RCDs (‘split load’). Best practice was to cover, say, upstairs lights and downstairs sockets with one RCD, and vice versa on the other. So if you were using something that caused a trip, your floor’s lights would stay on an enable you to find a torch. Also, if you had the right kind of earthing system, you could have a few ‘privileged’ circuits not covered by either RCD, where you could put ovens and other things liable to nuisance trip, or a freezer. However, it’s pretty much all RCBOs now.

 

[Wrichik Basu]

Are RCBOs available where you are?

Yes, but the price is twice the total price of an MCB and RCCB of the same rating. Only available on Amazon, they have bad ratings and people have said that they get faulty pretty soon. Not worth buying.

 

[Guineafowl]

Yes, but the price is twice the total price of an MCB and RCCB of the same rating. Only available on Amazon, they have bad ratings and people have said that they get faulty pretty soon. Not worth buying.

Fair enough. Decent ones are pretty easy to get here, and the price is not too bad, both due to demand, I guess.