Is there a facility to remotely trip a RCCB/RCD? I'd like to put an emergency power off button on my server room and am wondering if I really need an RCCB/RCD /and/ a contactor?
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I take it you do not want the ability to turn the room back on again? Also, I take it your EPO button is a Normally Open type?– ThreePhaseEelJan 10, 2018 at 2:24
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1. No, its in case of fire, for example. 2. That I'd have to check, should I be able to find such an RCCB– IanJan 10, 2018 at 2:56
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1RCCBs are not extremely reliable - certainly less so than a normal breaker. What happens when the emergency cutoff doesn't work?– SomeoneSomewhereSupportsMonicaJan 10, 2018 at 4:55
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That comment is working on the assumption that you want to trip it directly, i.e. with earth leakage. Other ways are probably fine.– SomeoneSomewhereSupportsMonicaJan 10, 2018 at 5:05
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@SomeoneSomewhere I'd be worried if a safety solution was not reliable, but your point is taken.– IanJan 10, 2018 at 18:43
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3 Answers
You need an extra option for this
Assuming your EPO switch is a normally open type, the typical way to do this at the panel uses a breaker with a shunt trip or shunt release option fitted, which will trip the breaker when power is applied to the shunt trip's terminals. Most North American panelboard-type MCBs can be ordered with a shunt trip as a factory option -- however, it's limited in nature, and often cannot be applied to specialty breakers such as GFCIs/AFCIs.
However, what you can do is provide GFCI, GFPE, or AFCI protection for the branch circuits, and put the shunt trip on the main or feeder shutoff breaker. That way, you only need one custom-ordered breaker instead of several, and also circumvent the incompatibility between specialty breakers and shunt trip accessories.
If you were back home...
If you were on the European system, however, DIN rail breakers are rather modular (compared to North American loadcenter/panelboard-type MCBs), so shunt trips for RCCBs are available as a general rule. Most can be either factory or field fitted depending on the situation and breaker make/model.
(If you had a normally closed EPO, you'd need an undervoltage release option instead -- it's the inverse function of a shunt trip. These are not as common as shunt trips, especially in North America although some European breaker lines have restrictions on the employment of their undervoltage release options that aren't present on their shunt trips.)
answered Jan 10, 2018 at 4:05
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Thanks for this, this sounds like the best option. I'm actually doing this in Colombia, which broadly uses the US system but without, as far as one can tell, any regulations (or at least their enforcement). So a DIN module solution will probably be impossible to find, or at least expensive. I'll see if I can find something I can install in the loadcenter.– IanJan 10, 2018 at 18:42
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@Ian -- what make/model is the loadcenter? Also, why are you calling it a RCCB? Are we talking about a GFCI or GFPE breaker, or are you simply calling it a RCCB because you don't know what to call it? Jan 10, 2018 at 23:29
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I'm British. I think we call them RCCBs or RCDs there, whereas Americans call them GFCIs. Same thing, I think? Under construction. I'm running totally new cabling back to the meter so I can put in anything I want, or at least anything I can find. Typical options seems to be: homecenter.com.co/homecenter-co/search/… I'd love to go DIN but it would make maintenance a bitch...– IanJan 10, 2018 at 23:56
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@Ian -- is there a reason you're putting a GFCI or GFPE device on a server room branch circuit? It seems like a strange application...although yes, a UK RCCB (RCBO) is basically equivalent to a North American GFPE breaker. (The North American GFCI is available both in breaker and yoked form factors, and is basically the most sensitive GF device you'll run into, several times more sensitive than a GFPE or RCBO/RCD.) Jan 11, 2018 at 0:53
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In Britain it's usual to put an RCCB on pretty much everything. Best practice, iiuc, is an RCBO per circuit, but usual practice is an RCCB on a group of a few breakers. As some of the equipment in this room will be 1400W and needs to run continuously, I want to put an RCCB on each of those devices so if one fails it won't (or at least might not) affect the others. I'll check out the difference between GFCIs and GFPEs, thanks.– IanJan 11, 2018 at 1:14
You could use a RCD tester. This is a device which places a sensibly sized load between hot and ground, aiming to induce more fault current than the RCD's trip threshold, proving the RCD works.
You could make one yourself out of a big red pushbutton switch and a right sized resistor. Take the RCD's current rating (e.g. 30ma), multiply by 5 to get a nice sure trip, that is I (current). You know your mains voltage, that is E (voltage). Apply Ohm's Law E=IR, solve for R and your resistor value pops out. Size (wattage) of resistor: apply Watt's Law EI=W.
answered Jan 10, 2018 at 18:21
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For the original poster and subsequent readers, I want to first clarify the terms used and summarise the purpose of each item, which should then help answer the question.
- RCD = Residual Current Device
- RCCB = Residual Current Circuit Breaker
- RCBO = Residual Current Circuit Breaker with Overcurrent/Overload Protection
RCD and RCCB are two names for the same item. These terms are typically used in the UK to refer to a current-operated fault detector. If Line/Phase voltage does not equal Neutral voltage under load, current is leaking to earth/ground, possibly through someone's body. By breaking the circuit within defined tolerances of current and time, potential electric shock is avoided. An RCBO combines the function of an overcurrent device like a thermo-magnetic miniature circuit breaker or a fuse, with that of an RCD.
In North American terminology, the RCD is equivalent to a GFCI = Ground Fault Circuit Interruptor. GFPE = Ground Fault Protection Equipment has higher tolerances and a different purpose: the detection of earth/ground leakage that could damage an appliance but that is insufficient to operate an overcurrent device (e.g. a fuse). The equivalent to an RCBO is a GFCI 'breaker'.
In terms of remotely testing an RCD and thus intentionally causing it to operate (trip), one product I found from an Australian company is the Rapid Test RTTUWF RCD Test Module with Wi-Fi communications, so such devices do exist. This will be safer than a DIY solution to deliberately create imbalance between phase and neutral.
Of course, you'll need extant power to operate any such test device and the network used to trigger it, so it would need to be isolated from the RCD and/or connected to a UPS. It's unclear whether something similar exists for the 110V/60Hz system in Colombia, but the US market may have something designed for this purpose at these voltages.
Remember, the RCD test function is intended to test the device, not to reliably operate it. Its purpose is to verify whether the RCD will operate, which in some cases, it may not. Therefore testing is not a reliable way to de-energize the circuit.
This is the function of an Emergency Power Off (EPO) switch, so that should clearly answer your question of whether you need both - yes, you do. Depending on your purpose for the EPO, you may need a switch or similar device at the power to the UPS and/or from it. APC does offer remote EPO systems for data centers, but this may be overkill.
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A fellow SA expat! Nice. I'm no expert in these matters but I think that RCD is an umbrella term that includes both RCCBs and RCBOs? Also, I think your description of their operation may apply to the predecessor ELCB devices: iiuc the RCDs detect current imbalances, not voltage. The GFCI device seems to trip at a /much/ lower leakage current than an RCCB: iirc 2mA v 30mA but that GFPEs (or is it GFEP? I've seen both) can have varying current and time delays, including 30mA/instant. Why are they so expensive though? Your comments about using RCD test and EPO positioning are noted, thanks.– IanJan 11, 2018 at 2:43
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You're welcome. Typically RCD refers to RCCB but there are so many terms it can be confusing even to the initiated. ELCBs connected to earth and measured actual leakage to the main earth cable, but that doesn't detect leakage through a body that bypasses the earthing, hence my mention of 'current-operated' and difference between L and N voltages under load. It's detecting voltage, but operating based on current. I can't comment on expense in Colombia, maybe import taxes to make up for the illegal drug trade laundering money? ;-) Jan 11, 2018 at 2:53
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Ah, understand. I was looking at US prices for now: finding product in Colombia is difficult at the best of times and local policy is not to give even a hint of the price in case someone might actually want to buy it... I've now found that GFCI yokes are comparable in price (US anyway) to UK RCDs. I guess there's limited demand for the GFPEs?– IanJan 11, 2018 at 4:17
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Is it OK to use a GFCI on a circuit without a ground connection? No idea about code here but it's rare to find premises in Colombia with a functional 3rd earthing pin. And putting in a grounding rod would mean drilling through a concrete floor. And then I've no idea what the water table depth might be.– IanJan 11, 2018 at 4:20
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Same here in Mexico - yes, as an RCD measures leakage from phase/neutral rather than to a ground wire like the old ELCBs did, they don't require an earth connection and will still trip on leakage to earth whether by way of an earth wire, pipes, conductive building materials or a human body, and you'll still see the safety benefits (hopefully not literally) Jan 11, 2018 at 5:16