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Generator - connection of neutral and ground wire.
Hi,
Both Charles Wing and Nigel Calder allude to connecting the neutral and ground wire of AC generators at the generator. Both authors also show alternator generators with a centre tap at 0v and the other two conductors at +60/120v and -60/120v (giving 120 and 240v respectively). The 0v centre tap I think is connected to ground, but is one of the conductor wires really connected to the ground??? Both authors have produced diagrams with no ground/conductor connection shown. It seems a little odd - grateful for clarification. TVMIA |
Generator - connection of neutral and ground wire.
"Rob" wrote in message om... Hi, Both Charles Wing and Nigel Calder allude to connecting the neutral and ground wire of AC generators at the generator. Both authors also show alternator generators with a centre tap at 0v and the other two conductors at +60/120v and -60/120v (giving 120 and 240v respectively). The 0v centre tap I think is connected to ground, but is one of the conductor wires really connected to the ground??? Both authors have produced diagrams with no ground/conductor connection shown. It seems a little odd - grateful for clarification. TVMIA Yeah like " I can't be bothered reading books or studying, would someone please tell me in less than 25 words all about electricity. In particular AC theory which can't be all that complicated since there are so many electricians doing it. Not like it's difficult like real technicians who fix TV's and things" -- Regards ............... Rheilly Phoull |
Generator - connection of neutral and ground wire.
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Generator - connection of neutral and ground wire.
Yeah like " I can't be bothered reading books or studying, would someone
please tell me in less than 25 words all about electricity. In particular AC theory which can't be all that complicated since there are so many electricians doing it. Not like it's difficult like real technicians who fix TV's and things" A particularly useful contribution - and I have been reading the books - hence the question. If you have not got anything worthwile to say that adds to the discussion, then don't bother cluttering up the listing with your drivel. |
Generator - connection of neutral and ground wire.
There are some simple rules to follow. The only problem is they may be
difficult to implement in some cases. Rule #1 For safety reasons, all AC systems need to have the neutral and ground tied together. Rule #2 The neutral and ground must be tied together at ONLY one place. Rule #3 If you are connected to shore power, without an isolation transformer in your vessel, the neutral and ground will be tied together at the shore-side service panel. Rule #4 If you are connected to shore power, as in rule 3, you MUST NOT have the neutral and ground connected together aboard your vessel. Rule #5 If you have an AC generator, of any voltage, the neutral and ground should be connected together at the generator. Rule #6 If you have a true isolation transformer on board with the shore power connected to the input and the output feeding the loads on your vessel, then you have created a 'separately derived system'. In this case, you would connect the neutral output of the transformer to the vessel ground to satisfy Rule #1. Notice Rule #4 says you must not have neutral connected to ground aboard your vessel and Rule #5 says they should be connected together. This is where it gets tricky. The easiest way to not break either rule is to have a two-pole circuit breaker for the shore power and another one for the generator. Each of these breakers disconnects the 120 volt hot lead AND the neutral lead from it's source. These breakers must be mounted together with a mechanical slide that will only allow one of the breakers to be ON at a time. The output of these breakers supply the hot and neutral to all on-board loads. By only having one breaker ON at a time you keep the grounded neutrals apart and satisfy all the rules. An added benefit is you also keep shore power and your generator output separate. If your shore power is 120/240 volt and your generator is the same, then the two breakers would be three-pole units. Each breaker would disconnect both hot leads and the neutral from it's source. If you have an inverter/charger and a generator on board then the whole thing gets a lot more complicated. You still have to follow all the above rules. There are various ways to do this, some simple, and some complicated. Trace Engineering, now Zantec, will send you a relay switching diagram if you ask for it. If your single-phase generator is set up to put out two voltages, such as 120/240 volts, then the zero volt center tap IS the neutral and the only lead tied to ground. If a single-phase generator is set up to produce only a 120 volt output then the neutral is the zero volt output and again is the only wire connected to ground. If you have a three-phase generator, one of the output leads will be connected to ground. If a three-phase generator has a neutral output, it is connected to ground. If, and only if, a three phase generator is wired so as to NOT have a neutral output, then any ONE of the hot legs is grounded. This is the ONLY time a hot wire would be grounded. This is a very rare type of connection and would always be designed by an experienced marine electrical engineer. Most of my experience is with shore-based heavy industrial electrical systems, process control systems, and remote off-grid power systems. I have never seen a 60-0-60 volt generator. Nor have I seen equipment that is designed for 60 volts AC. I have seen generators of 120-0-120 volt and three phase generators of various higher voltages. My Northern Lights 5.5Kw marine generator can be wired to provide either a single 120 volt two wire output or 120/240 volt three wire output. Perhaps our questioner meant a 60 Hz 120 volt system where 60 refers to the frequency of the alternating current and 120 refers to the voltage. Rusty |
Generator - connection of neutral and ground wire.
On Sat, 27 Dec 2003 18:15:16 GMT, Larry wrote:
Being totally unfamiliar with naval systems, the question Rob asked still remains: Is the neutral (in a 60 - 0 - 60 system) connected to one of the 60 volt legs? Is it still coded white? I'm assuming that ground is always connected to frame or earth ground in any system. I'm sorry but I really don't remember. The last ship I was on with this was USS Everglades (AD-24) completed in 1952. I was on her from 1966-1969 and I'm WAY too old to remember details back THAT far, now.... But, as I remember doing some wiring in our calibration lab, I don't think there was a "neutral" in that system. The 120VAC was from one wire to another and I don't think the center tap of it was connected to anything but ship's ground, as we didn't use the 60VAC for anything to that center tap. |
Generator - connection of neutral and ground wire.
Many ships have ungrounded systems, with ground fault monitoring. Single
phase panels are used (without the neutral bus), or three phase panels (120 volt delta). All circuits use 2 pole breakers. Common ground monitor is lights from phase to ground, if the light is out the phase is grounded. Pete Albright, Tampa, FL "Larry W4CSC" wrote in message ... On Sat, 27 Dec 2003 18:15:16 GMT, Larry wrote: Being totally unfamiliar with naval systems, the question Rob asked still remains: Is the neutral (in a 60 - 0 - 60 system) connected to one of the 60 volt legs? Is it still coded white? I'm assuming that ground is always connected to frame or earth ground in any system. I'm sorry but I really don't remember. The last ship I was on with this was USS Everglades (AD-24) completed in 1952. I was on her from 1966-1969 and I'm WAY too old to remember details back THAT far, now.... But, as I remember doing some wiring in our calibration lab, I don't think there was a "neutral" in that system. The 120VAC was from one wire to another and I don't think the center tap of it was connected to anything but ship's ground, as we didn't use the 60VAC for anything to that center tap. |
Generator - connection of neutral and ground wire.
Larry W4CSC wrote:
However, on ships, to reduce the voltage to ground reducing shock hazards on 120V power systems, there IS a 60-0-60 system with a center-tap-grounded power system. I used to serve on old Navy ships that had this system. Not sure if they still use it on new ships, now. There was never a "60-0-60 system" on ships. Nearly every ship generates 3-phase power and for hotel services requiring 120VAC the phase transformers are wired in wye-delta providing 3 conductors each of 120 volts between any two conductors. The voltage measured to ground would be either about 87 volts or 70 volts depending on the phase which is measured against the ship's ground. When 120/208 power is required the phase transformers are wired in delta-wye with a 4th neutral conductor connected to physical ground. Any conductor measured to ground would deliver 120 volts single phase. The voltage between conductors is 208 volts 3-phase. This is not commonly supplied to "hotel" services as it is preferable to reduce shock hazard via the lack of a grounded neutral and to avoid using the hull as a current carrying ground. Rick |
Generator - connection of neutral and ground wire.
In article ,
"PeteAlbright" wrote: Many ships have ungrounded systems, with ground fault monitoring. Single phase panels are used (without the neutral bus), or three phase panels (120 volt delta). All circuits use 2 pole breakers. Common ground monitor is lights from phase to ground, if the light is out the phase is grounded. Pete Albright, Tampa, FL "Larry W4CSC" wrote in message ... On Sat, 27 Dec 2003 18:15:16 GMT, Larry wrote: Being totally unfamiliar with naval systems, the question Rob asked still remains: Is the neutral (in a 60 - 0 - 60 system) connected to one of the 60 volt legs? Is it still coded white? I'm assuming that ground is always connected to frame or earth ground in any system. I'm sorry but I really don't remember. The last ship I was on with this was USS Everglades (AD-24) completed in 1952. I was on her from 1966-1969 and I'm WAY too old to remember details back THAT far, now.... But, as I remember doing some wiring in our calibration lab, I don't think there was a "neutral" in that system. The 120VAC was from one wire to another and I don't think the center tap of it was connected to anything but ship's ground, as we didn't use the 60VAC for anything to that center tap. Pete is correct in that some on board wiring deletes the netral to earth bonding altogether. In this situation you loose the fault current protection generated when there is a fault from active to conductive case of equipment. In this instance it is absolutely imperative to have Residual Current Devices (RCD's) or GFI in NA parlance both on the shore power inlet and the onboard generator. I just did an electrical survey on a boat where this was the case. BTW downunder we have 240/408 single/3 phase 50 Hz systems. John Proctor -- John VK3JP |
Generator - connection of neutral and ground wire.
"Rusty O" wrote in message hlink.net... There are some simple rules to follow. The only problem is they may be difficult to implement in some cases. Rule #1 For safety reasons, all AC systems need to have the neutral and ground tied together. Rule #2 The neutral and ground must be tied together at ONLY one place. Rule #3 If you are connected to shore power, without an isolation transformer in your vessel, the neutral and ground will be tied together at the shore-side service panel. Rule #4 If you are connected to shore power, as in rule 3, you MUST NOT have the neutral and ground connected together aboard your vessel. Rule #5 If you have an AC generator, of any voltage, the neutral and ground should be connected together at the generator. Rule #6 If you have a true isolation transformer on board with the shore power connected to the input and the output feeding the loads on your vessel, then you have created a 'separately derived system'. In this case, you would connect the neutral output of the transformer to the vessel ground to satisfy Rule #1. Snipped the rest of this wonderful material . . . Brilliant, Rusty. The most concise presentation of AC grounding I've seen. Many thanks. -- Jim B, Yacht RAPAZ, Sadly, for sale: http://homepage.ntlworld.com/jim.bae...cification.htm jim[dot]baerselman[at]ntlworld[dot]com |
Generator - connection of neutral and ground wire.
Rusty,
Thanks very much - and I think I've sorted out my confusion. The books are written from a US perspective and they are talking about the US 4 wire system - 2 hot wires, a neutral at 0v and ground. So it makes sense to ground the neutral. When read from a UK perspective with only a 3 wire system, then it makes no sense to ground the neutral, which is a hot wire. I've since found an excellent web search searching through this group which has some really usefull wiring schematics - which also confirms that it is a real snakes' wedding with 400v, 240v, 24v and 12v systems!!! Colin |
Generator - connection of neutral and ground wire.
On Sun, 28 Dec 2003 01:13:43 GMT, "PeteAlbright"
wrote: Many ships have ungrounded systems, with ground fault monitoring. Single phase panels are used (without the neutral bus), or three phase panels (120 volt delta). All circuits use 2 pole breakers. Common ground monitor is lights from phase to ground, if the light is out the phase is grounded. Pete Albright, Tampa, FL Now that you mention it I do think I remember a light on our knife-switch/screw-in fuse panel (black bakelite with wooden safety leaning bar), that alerted you to any current to the deck, indicating a fault. The cal lab had a Detroit Diesel, naturally-aspirated 6-71 2-stroke diesel driving a DC generator that originally powered the stern gun mount and director, which was removed when the disasterous DASH anti-sub helicopter was installed. The DC powered a big motor-alternator through a separate manual panel to create 60 Hz, 3 phase, 440 VAC that was fed to a bank of transformers buzzing away in the cal lab to keep us awake at night. All our Edison Lights were run directly from 110 VDC from the DC panel through a couple of knife switches....as Edison intended. The whole ship would go dark because of the Electical gang's incompetence a few times per voyage. The separately-powered cal lab shone like a beacon in the dark, then....(c; Larry ET1 Shop 67B, Calibration Lab USS Everglades (AD-24) Charleston, SC (1966-1969) Electricians were not allowed to have keys to OUR generator room.....hee hee. They never gave us keys to THEIR generator rooms, after all. It was only fair. In the Med, we used to turn the motor speed on the alternator down and run the cal lab on 50 Hz to keep the TV picture from pulsing at 10 Hz from the differences in scan frequencies and power supply hum....(c; I still have reel-to-reel tapes with 50 hz hum on them! |
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