What are these symbols? - Page 1
Forum section: electronics / beginners

author: semaphore
author_rank: Contributor
timestamp: February 26, 2011, 03:48:37 am
content: What is the two squares and house symbols mean? They are on the wall adapter.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 26, 2011, 03:51:13 am
content: maybe the house means use indoor.

author: GeoffS
author_rank: Unknown
timestamp: February 26, 2011, 03:54:04 am
content: The two concentric squares indicated that the device is doubly insulated to Class II and should not have an earth connectionCan't say I've ever seen the house symbol..

author: semaphore
author_rank: Contributor
timestamp: February 26, 2011, 04:05:10 am
content: Many thanks

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: February 26, 2011, 05:54:33 am
content: Quote from: Mechatrommer on February 26, 2011, 03:51:13 am"Indoor use only", you were correct

author: Neilm
author_rank: Super Contributor
timestamp: February 26, 2011, 10:15:27 am
content: Quote from: GeoffS on February 26, 2011, 03:54:04 amA double insulated product is allow to have an earth connection as long as it is for functional purposes only, not safety. An example would be a SMPS where and earth connection was used for EMI filtering.YoursNeil

author: Simon
author_rank: Unknown
timestamp: February 26, 2011, 10:23:15 am
content: To be honest I do not agree with this double insulation lark and no earth. I have an electric chain saw with no earth and is "double insulated", sure until I cut the cable and make the blade live, of course I'd not know a thing about it as the blade is not earthed. Of course if i were to touch the blade or later pick up the cable not knowing it is cut I'd be dead, instead if the blade were earthed it would trip the RCD immediately and I'd find the fault quikly

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 26, 2011, 10:53:13 am
content: Quote from: Simon on February 26, 2011, 10:23:15 amyou could be dead if you got electrocuted while operating the the "live" chain saw. but i'm not so certain, if you try to touch the cut cable only.

author: ziq8tsi
author_rank: Regular Contributor
timestamp: February 26, 2011, 01:51:43 pm
content: Quote from: Simon on February 26, 2011, 10:23:15 amI would recommend against touching the blade of a chainsaw in any circumstance! However, an RCD will drastically reduce your chance of being electrocuted, regardless of whether the device is earthed.Class I appliances can be miswired, the protective earth conductor can fail silently, or it can be defeated for wiring convenience or to resolve ground loop noise. Double insulation is inherently safe.

author: Simon
author_rank: Unknown
timestamp: February 26, 2011, 03:21:06 pm
content: I'm fine with double insulated stuff, but I'd still earth metal parts, especially on power tools

author: bill.rowland
author_rank: Contributor
timestamp: February 26, 2011, 04:31:15 pm
content: ALL CLASS 2 POWER TOOLS WERE FLASH TESTED TO 3750V TO TEST INSALATION BEFORE BEING RETURNED TO THE CUSTOMER AFTER REPAIR. ALSO WE ALWAYS ADVISED THE USE OF A 10MA RCD PLUG ADAPTOR AS 30MA CAN BE TO SLOW FOR OUTDOOR POWER TOOLS THE RCD SHOULD TRIP BEFORE THE BLADE WILL BECOME LIVE WE HAVE HAS MANY CLASS 1 EARTHED POWER TOOLS COME IN FOR REPAIR WITH DEFECTIVE EARTH CONECTIONS USALY THE PLUG HAS BEEN PULLED AND THE EARTH DISCONECTED , HIGH RESITANCE SO FAILPAT TESTI HAVE EVEN SEEN THE EARTH DISCONECTED ON A METAL CASE DRILLBILL

author: Simon
author_rank: Unknown
timestamp: February 26, 2011, 04:59:11 pm
content: so explain this with your RCD: an otherwise non connected saw blade goes through a live cable, the blade is now live but is not connected to earth in any way (by earth wire, human contact or other body), how will the RCD trip ? RCD's trip when a small current leaks to earth, there is no leak path how will it trip ?

author: Zero999
author_rank: Super Contributor
timestamp: February 26, 2011, 06:45:52 pm
content: Bill,Quote from: Simon on February 26, 2011, 03:21:06 pmIt depends on the situation.Often it's better if the operator is away from any earthed objects as there's no risk of a shock, in other situations it's better to earth.The only think I can think of is when a drill is used to drill a hole in the wall and the bit hits a live conductor. Then it doesn't matter whether the circuit powering the drill has an RCD or not, if it's not earthed the user will receive a shock if they touch any metal parts of the drill which could even be powered off a battery.Another, safer method of providing protection against electric shock is to power the tool from an isolation transformer, although using an earthed tool is the only way to protect against the above scenario.

author: Simon
author_rank: Unknown
timestamp: February 26, 2011, 07:08:41 pm
content: any cutting tool should have earthed metal parts, in the event of contact with live wires/parts the RCD will trip instantly (rather than later) and allow you to know exactly when contact was made and with what rather than stumble on a live part later

author: Zero999
author_rank: Super Contributor
timestamp: February 26, 2011, 07:20:54 pm
content: Quote from: Simon on February 26, 2011, 07:08:41 pmI wouldn't say it should always be earthed for the following reasons:If the drill is earthed and the circuit you make contact with is not protected by an RCD you would receive a shock.It's not always practical, a cordless drill can't be earthed and earthing a mains drill with a plastic body and nylon gears isn't easy.

author: Simon
author_rank: Unknown
timestamp: February 26, 2011, 07:39:20 pm
content: yes well there was a time we made stuff out of metal. I would hope that RCD's were brought in by the tie double insulation came about. These days any mains system is supposed to be protected by RCD's, it can't be all ways, a set system has to be followed, either way contact with a live part is dangerous, if in the case of the drill the fault will remain unknown and a breached wire in a wall could catch fire later, if the drill is earthed the RCD will cut immediatly alerting to the fault, if you were to touch the live chuck (that now will be live as not being earthed) then YOU will be the path for the earth fault that blows the RCD, if there is no RCD you'r be dead anyhow.With no RCD and fuses only the drill bit/chuck not being earthed will not provide the fault current to blow the fuse, You touch the live chuck and it will kill you because it takes just 30mA to kill you and the fuse blows at 13 A - your long dead by then.

author: bill.rowland
author_rank: Contributor
timestamp: February 26, 2011, 08:54:36 pm
content: i was told a rcd mesures the p / n ballance ? How will a rcd still trip if it is a class 2 item if it needs a earth path to trip? This is the way we were tought in the tool rental trade pat test / flash test before rerental but i have been out of it for 13 years so things may have changed

author: Zero999
author_rank: Super Contributor
timestamp: February 26, 2011, 09:14:45 pm
content: Yes, an RCB measures the difference in current between the live and neutral.Simon,My point is that if you're holding an earthed tool you're at greater risk of receiving a shock from another piece of electrical equipment than if you have a high impedance to earth.

author: FreeThinker
author_rank: Frequent Contributor
timestamp: February 26, 2011, 09:16:35 pm
content: Quote from: Simon on February 26, 2011, 07:39:20 pmRCD residual current device, does what it says on the tin trips if there is a residual or fault current. If you got hold of the live wire and earthed yourself then the RCD would see an imbalance in the current between live and neutral and trip REGARDLESS of if the device is earthed or not. Double insulated are inherently safer because they do not rely on an earth bond to be safe unlike a earth bonded device which can become unsafe if the earth bond fails. The RCD protects the sub circuit not the device.AS you point out if no rcd is fitted then the sub circuit becomes dangerous and the only protection is the fuse, but this is not a problem with the device but with the final sub circuit.Most modern homes have both rcd and elcb (earth leakage) protection

author: Simon
author_rank: Unknown
timestamp: February 26, 2011, 09:16:44 pm
content: The RCD detects a fault to earth, which may be through an earthed part or through the human body. What I'm saying is just because you use RCD's does not mean that earthing is not required, as i just explained if you have a non earthed drill chuck and hit a wire it won't trip the RCD, it only will if you touch the chuck as you will earth it. Just because we use plastic does not mean we don't need an earth

author: Simon
author_rank: Unknown
timestamp: February 26, 2011, 09:25:44 pm
content: With an earthed chuck:NO RCD: The main fuse blows because you have made a direct short from live to earth, if you do touch the chuck it is at 0V so your safewith RCD: the RCD cuts as soon as you hit the wireWithout earthed chuck:With RCD: will trip only if you touch the chuck, or the wall acts as an earth drainwithout RCD: Chuck is live, you touch it you dieAmen !

author: RayJones
author_rank: Frequent Contributor
timestamp: February 26, 2011, 09:42:06 pm
content: Quote from: Simon on February 26, 2011, 09:16:44 pmNo they don't.They detect an imbalance in active neutral currents, typically by winding each line around a toroid in anti phase. The net magnetic field should then be zero.If you imbalance the currents, there is a residual magnetic field generated, which induces volts into a third winding, which ultimately pulls the pin on the circuit contacts.Earth is only involved in an indirect manner as to the reason why we got an initial imbalance.As for drilling into walls and collecting the mains by accident, are you also proposing all cordless drills require a trailing earth wire?If your petrol powered chainsaw cuts a power lead, should it be earthed also?All the same scenario using devices that are not mains powered. You can only protect against certain forms of stupidity.

author: Zero999
author_rank: Super Contributor
timestamp: February 26, 2011, 09:48:56 pm
content: Quote from: RayJones on February 26, 2011, 09:42:06 pmYes I was trying to say that earlier on.And if you're holding an earthed drill and you touch a live wire or another piece of equipment which has developed a fault, you'll definitely receive a nasty of not lethal shock, on the other hand if the drill isn't earthed you might not get shocked at all.

author: Simon
author_rank: Unknown
timestamp: February 26, 2011, 09:55:07 pm
content: well it sounds like a cordless drill is not a good option when you suspect wires are in the wall.If your using a petrol chainsaw near live wires you deserve to die, unfortunately with an electric chansaw it's not an option.RayJones: As far as defining an RCD in our current hypothetical setup goes, in a long winded way you said exactly what I did, I presumed we all know the intricacies of how they work.

author: RayJones
author_rank: Frequent Contributor
timestamp: February 26, 2011, 10:10:16 pm
content: Sell the chainsaw on ebay and buy a petrol one then - that's the safest option then.Mains electricity in the garden is always dangerous.Yes, petrol chainsaws are smelly and noisy - and that is good for safety - you know it will bite if you pull the trigger when it is smelly and noisy.The electric one should be banned because it is silent and deadly.And if you suspect wires are in the wall, in reality using any form of tool is potentially dangerous. <pun intended>As for being long winded, I fail to see how you could define the RCD's operation mode any more simply in technical terms.If you had originally quoted "The RCD protects against a fault to earth" I would have let it go, but using "detects" implies it detects that earth fault directly. It doesn't.

author: Zero999
author_rank: Super Contributor
timestamp: February 27, 2011, 12:55:36 am
content: Quote from: Simon on February 26, 2011, 09:55:07 pmYou shouldn't use any drill if you suspect live wires in the wall. The safest thing to do is turn of the power and use a non-contact voltage detector just to make sure.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 27, 2011, 06:12:26 am
content: earthing mechanism is just one attempt in safety. but it will not keep you 100% safe, the other (major) factor, is human intelligence. i second RayJones. my 2cnts.Quote from: RayJones on February 26, 2011, 09:42:06 pm

author: Simon
author_rank: Unknown
timestamp: February 27, 2011, 07:45:35 am
content: Quote from: Hero999 on February 27, 2011, 12:55:36 amPower tools are sold all over the world, ever tried picking up a wire through solid rock ? in some countries walls are 2+ feet thick, you don't always know what is in there. If the earth does fail the RCD will protect you, after all if we go on the assumtion your doing it right and using a wire detector and doing it properly you'd also not be working without an RCD. Portable RCD's are also available. I use one on my saw

author: Zero999
author_rank: Super Contributor
timestamp: February 27, 2011, 09:29:04 am
content: Quote from: Simon on February 27, 2011, 07:45:35 amYes, it's possible with the gagit linked below.http://www.google.co.uk/products/catalog?client=opera&rls=en&q=non-contact+voltage+detector&oe=utf-8&channel=suggest&um=1&ie=UTF-8&cid=1052363795548288751&sa=X&ei=jBhqTcTQNceLhQfom9mhDw&ved=0CDUQ8wIwAA#QuoteWhat difference does that make? You won't be able to find a drill bit that long which will fit into an ordinary hand drill.QuoteNo it doesn't, if the wires in the wall are not protected by an RCD, it makes no difference whether your drill has RCD protection or not, if the earth fails and you hit a cable, the drill's case becomes live.

author: Simon
author_rank: Unknown
timestamp: February 27, 2011, 09:48:10 am
content: I have a dril 2 ft longit's a N10 for putting wires through walls, yes in the case of the drill a portable RCD won't protect. However it will protect the chainsaw. ike I said, there are different methods of protection and one only needs to be followed