Guest scottygio Posted November 26, 2005 Share Posted November 26, 2005 What is the rule in the running of alarm cable? I have only one route to get my alarm cables upstairs and the mains (230v) is running along the same route. So the two types of cables will run parallel to each other for about 3 metres after which i can seperate then fairly well. thanks in advance Scott Link to comment Share on other sites More sharing options...
Guest rjbsec Posted November 26, 2005 Share Posted November 26, 2005 The rule is don't do it, but for 3 metres you may get no problems ... on the other hand ....! If you must do it keep the cables as far apart as possible, or better still use screened cable and take the screen to earth inside the alarm panel. It is often possible to measure anything up to 100 volts AC on the DC alarm cable runs where they have been run near to mains cable - this is called "induced AC" and can be the source of all sorts of false alarm problems and even panel damage. In addition to the use of screened cable some suppliers provide filters that help to eliminate induced AC from cables by taking it to earth. Link to comment Share on other sites More sharing options...
jb-eye Posted November 27, 2005 Share Posted November 27, 2005 What is the rule in the running of alarm cable? I have only one route to get my alarm cables upstairs and the mains (230v) is running along the same route. So the two types of cables will run parallel to each other for about 3 metres after which i can seperate then fairly well. thanks in advance Scott No problem. You will however have to instal a barrier between the two. Quickest cheapest way of doing this is to install either catagory of cable within a containment such as a plastic trunking or pass the cables through a conduit.Jef Customers! Link to comment Share on other sites More sharing options...
Guest rjbsec Posted November 27, 2005 Share Posted November 27, 2005 The outer sheath of both mains and alarm cable is made of plastic material yet induced AC passes through the outer sheath of the mains cable and through the outer sheath of the alarm cable to be recorded on the wire cores of the alarm cable. Ask yourself, will a thin wall of plastic as found in conduit or trunking form any more of a barrier to the induced AC voltage? As I said above, it may cause you no problems but it is bad practice and should be avoided if at all possible - couple of quotes:- From David Grant - ACT Meters (UK): Next to user error, induced AC voltage caused by electro-magnetic interference (EMI) is the biggest cause of false alarms. Alarm cables running alongside mains, telephone and other service cables, induce high voltages and electrical Link to comment Share on other sites More sharing options...
dpaengineer Posted November 27, 2005 Share Posted November 27, 2005 The outer sheath of both mains and alarm cable is made of plastic material yet induced AC passes through the outer sheath of the mains cable and through the outer sheath of the alarm cable to be recorded on the wire cores of the alarm cable.Ask yourself, will a thin wall of plastic as found in conduit or trunking form any more of a barrier to the induced AC voltage? Errrrrrr, yes it it will actually. Hence it is specified in the BS 7671 regulations. Any Extra Low Voltage cables that are to run alongside Mains (Low Voltage) must be contained in conduit/trunking! Trade Member Link to comment Share on other sites More sharing options...
jb-eye Posted November 27, 2005 Share Posted November 27, 2005 Errrrrrr, yes it it will actually. Hence it is specified in the BS 7671 regulations. Any Extra Low Voltage cables that are to run alongside Mains (Low Voltage) must be contained in conduit/trunking! I wasnt going to go there but thanks anyway. At least someone may have learned something. ()Jef Customers! Link to comment Share on other sites More sharing options...
Guest rjbsec Posted November 27, 2005 Share Posted November 27, 2005 Errrrrrr, yes it it will actually. Hence it is specified in the BS 7671 regulations. Any Extra Low Voltage cables that are to run alongside Mains (Low Voltage) must be contained in conduit/trunking! I am always willing to learn and would be interested to be pointed to the exact reference in BS 7671 that declares that plastic trunking has the ability to remove the danger of induced AC voltages from alarm cables. I think it is very easy to underestimate the nuisance problems that induced AC can cause in alarms, which might not be experienced in other data and similar cabling - of course we are talking nuisance, not electrical safety here. Link to comment Share on other sites More sharing options...
jb-eye Posted November 27, 2005 Share Posted November 27, 2005 I am always willing to learn and would be interested to be pointed to the exact reference in BS 7671 that declares that plastic trunking has the ability to remove the danger of induced AC voltages from alarm cables.I think it is very easy to underestimate the nuisance problems that induced AC can cause in alarms, which might not be experienced in other data and similar cabling - of course we are talking nuisance, not electrical safety here. Im trying to e-mail you but cant find e-mail on your site. The forum is not allowing atttachments at the moment, anyway you should have BS7671 so look up reg 528-01-01 Jef Customers! Link to comment Share on other sites More sharing options...
Guest rjbsec Posted November 27, 2005 Share Posted November 27, 2005 Im trying to e-mail you but cant find e-mail on your site. The forum is not allowing atttachments at the moment, anyway you should have BS7671 so look up reg 528-01-01Jef Yes there seems to be some problems with email and PM's at the moment. Thanks for the reference I will check that out during the week ahead. Link to comment Share on other sites More sharing options...
Allso Posted November 27, 2005 Share Posted November 27, 2005 I am always willing to learn and would be interested to be pointed to the exact reference in BS 7671 that declares that plastic trunking has the ability to remove the danger of induced AC voltages from alarm cables. I share rjbsec's sceptical view on this one. It would defy the basic laws of physics for plastic trunking to remove the danger of induced AC voltages, no matter what any regulations might say! It's the magnetic fields around the AC cable that cause the induced voltages, and I can't see how plastic would protect alarm cables from this. Allso Link to comment Share on other sites More sharing options...
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