PROTECTION , ISOLATION , SWITCHING , CONTROL AND MONITORING

Question 1

devices for protection against electric shock by automatic disconnection of supply shall be suitable for isolation

pg 153&154.

Answer 1

for systems other than TN & TT , RCDs must disconnect all live conductors.
531.3.1.202 - it is to avoid damage and unintentional electric shock . reinforce no borrowed neutrals rule which would cause the rcd to trip.

Question 2

types of RCD. there r different types. type AC being the most common and is an rcd that will only detect ac faults.

Answer 2

type a, type b and type c rcd detect both AC & DC faults.

Question 3

RCDs for Fault Protection.

less sensitive rcd can be used by a 100 ma RCD.

155 and 156 and very top of 157

Answer 3

RCDs are generally to be located at the origin of the installation.
on the load side of RCDs , protective and neutral conductors must not be connected , otherwise the rcd may nuisance trip or simply not detect faults.

Question 4

devices for the protection against the risk of fire.

pg157.

Answer 4

RCDs with a rating not exceeding 300 ma should be used

Question 5

devices for protection against overcurrent.

pg 158

Answer 5

• Fuses to BS 88 series , BS 646 OR BS 1362
• Rewierable fuses. to BS3036
• Circuit Breakers and RCBOs to BSEN60898 , BSEN60947 AND 61009

Question 6

devices for protection against overvoltage

Answer 6

any question on Surge Protection Devices will be on section 534 of bs7671

Question 7

isolation and switching ; there are 4 main types of switch

table 537.4 on pg 181

Answer 7

• isolation e.g main switch in a consumer unit.
• maintenance - isolate a part of the circuit and lock it off so no one can turn it on
• functional - isolating a part of the circuit without isolating the whole circuit.
• emergency

Question 8

firefighters switch

wouldn’t see them in domestic properties

Answer 8

ables the fire brigade to come in and isolate the installation when there’s a fire.
can find firefighters switches in petrol stations @ a certain height.
must comply with been 60669.

Question 9

monitoring devices ( IMDs)

section 538
wouldn’t see them in domestic properties

Answer 9

mainly installed in IT earthing arrangements ( where we want to avoid automatic disconnection of supply in the event of a fault so instead we use a Monooring device that detects a latent fault ( a fault that’s not fully developed)