Can medium duty conduit be run underground (without the concrete encasing that makes it a Cat A system) as a Cat B system?
I can only see an option for corrugated or flexible
Medium duty conduit underground Table 3.5
Re: Medium duty conduit underground Table 3.5
Short answer: yes.
Correct that, for all listed types of cable; if installed in MD conduit and encased on concrete the wiring system is classified as Cat A (column 3 of the Table).
Without the concrete, whether it's Cat A or Cat B depends on cable type (column 7).
I think you've perhaps missed the comma in Col 7 heading;
At first glance, this comma may appear to be simply a separator between item 1 "medium duty" and item 2 "corrugated"; with item 3 being "flexible". However that's not a correct interpretation.
While Table 3.5 is a handy reference; it's primarily intended to tell us whether a particular combination of cable type and protection method is permitted.
The citation for the Table is in 3.11.2 ; where Para 6 sets two requirements:
- it says the cable type must be one of those listed in the Table; and
- it then requires the cable to be installed in accordance with a category of installation permitted by Columns 2- 9.
So while column 1 specifically limits the types of cable that may be used underground; row 1 does not specifically limit the types of protection.
Indicating the Category is a secondary function of the Table; because the actual descriptions for each Category are in the respective clauses.
Preceding paras of 3.11.2 state that the essential difference between cat A & Cat B is whether additional mechanical protection is required; and this is based on whether the cable type is "inherently suitable" for use underground; or only suitable for use underground with additional protection for either the cable itself or the cable enclosure.
Following sub-clauses give specific descriptions for each Category;
3.11.3.1(a) specifies that any form of heavy duty insulating conduit is Cat A, regardless of cable type.
(b) says that an insulating wiring enclosure encased in concrete is also Cat A (MD conduit being an example).
Your specific query WRT MD conduit is covered in 3.11.3.2 (a); being classified as Cat B - again regardless of cable type.
And, because it's Cat B, it then also needs additional protection by a method listed in 3.11.4.3.
The conduit isn't part of the "additional protection"; it's part of the "wiring system".
Worth noting that while TPS can be buried directly, adding MD conduit doesn't change the category; it's still B.
What it does achieve is avoid the need for the bedding that's required for unenclosed cables by 3.11.4.2
Or if we upgrade to HD conduit; it becomes Cat A, and then no additional protection needed.
Correct that, for all listed types of cable; if installed in MD conduit and encased on concrete the wiring system is classified as Cat A (column 3 of the Table).
Without the concrete, whether it's Cat A or Cat B depends on cable type (column 7).
I think you've perhaps missed the comma in Col 7 heading;
At first glance, this comma may appear to be simply a separator between item 1 "medium duty" and item 2 "corrugated"; with item 3 being "flexible". However that's not a correct interpretation.
While Table 3.5 is a handy reference; it's primarily intended to tell us whether a particular combination of cable type and protection method is permitted.
The citation for the Table is in 3.11.2 ; where Para 6 sets two requirements:
- it says the cable type must be one of those listed in the Table; and
- it then requires the cable to be installed in accordance with a category of installation permitted by Columns 2- 9.
So while column 1 specifically limits the types of cable that may be used underground; row 1 does not specifically limit the types of protection.
Indicating the Category is a secondary function of the Table; because the actual descriptions for each Category are in the respective clauses.
Preceding paras of 3.11.2 state that the essential difference between cat A & Cat B is whether additional mechanical protection is required; and this is based on whether the cable type is "inherently suitable" for use underground; or only suitable for use underground with additional protection for either the cable itself or the cable enclosure.
Following sub-clauses give specific descriptions for each Category;
3.11.3.1(a) specifies that any form of heavy duty insulating conduit is Cat A, regardless of cable type.
(b) says that an insulating wiring enclosure encased in concrete is also Cat A (MD conduit being an example).
Your specific query WRT MD conduit is covered in 3.11.3.2 (a); being classified as Cat B - again regardless of cable type.
And, because it's Cat B, it then also needs additional protection by a method listed in 3.11.4.3.
The conduit isn't part of the "additional protection"; it's part of the "wiring system".
Worth noting that while TPS can be buried directly, adding MD conduit doesn't change the category; it's still B.
What it does achieve is avoid the need for the bedding that's required for unenclosed cables by 3.11.4.2
Or if we upgrade to HD conduit; it becomes Cat A, and then no additional protection needed.
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