- October 9, 2026
- Posted by: Aceget
- Category: RECD & Emission Control Devices
On most RECD projects, one sheet of paper ends up carrying more decisions than any other. The site engineer checks it for space. The structural consultant checks it for loads. The electrician looks for the controller position. The safety officer looks for hot surfaces and access. The client signs it. The fabricator builds from it, and the maintenance team inherits it. That sheet is the general arrangement drawing, usually shortened to GA.
A good GA answers most questions before anyone asks them. A weak one, a neat outline of the device with a few dimensions and the word “tentative” in the title block, pushes every unresolved question onto the installation crew, who answer them with a grinder and a tape measure on the day.
This article sets out what an RECD GA drawing should contain, organised as twelve blocks of information. It then gives a reviewer’s red-pen checklist, lists the common gaps and follows a drawing through three revisions to show how review improves it.
What a GA Drawing Is, and What It Is Not
An engineering drawing can serve many purposes. The GA has a specific one: to show how the parts of an installation fit together in their real setting, with enough information to approve the layout and coordinate the trades.
| Document | Purpose | Relationship to the GA |
|---|---|---|
| General arrangement drawing | Overall layout, positions, envelopes, interfaces, key dimensions | The master coordination sheet |
| Fabrication or shop drawings | Detailed parts for manufacture: cut lengths, weld details, hole positions | Derived from the GA |
| Support and frame drawings | Steel members, connections, base plates, anchors | Referenced by the GA |
| Single-line diagram and wiring diagrams | Electrical supply and controls | Interfaces shown on the GA |
| Isometric exhaust route drawing | Three-dimensional pipe route for fabrication | Consistent with the GA |
| Device data sheet | Device ratings, materials, performance | Key values repeated on the GA |
The GA does not need every weld symbol. It does need to be the drawing that, if everyone follows it, makes all the others fit.
The Twelve Blocks of a Complete RECD GA
Block 1: Title block and revision history
The title block is not decoration. It tells the reader what they are looking at and whether it is current.
Should include:
- Project name, site address and DG set identification (make, model, serial number, rating)
- Drawing number and sheet number
- Revision letter or number, with date
- Status: for comment, for approval, approved for construction, as-built
- Drawn, checked and approved names or initials
- Scale for each view, and a note that the drawing should not be scaled where dimensions are given
Revision table: each revision should list what changed, briefly. “Rev B: device moved 600 mm east to clear AHU intake; sampling ports lowered to 7.2 m” tells the reader exactly where to look. “Rev B: general update” tells them nothing.
Accurate DG identification links the drawing to the device approval. Our guide on DG nameplate photos for an RECD enquiry explains what details matter.
Block 2: Views
A GA usually needs more than one view to show a three-dimensional installation clearly. Multiview orthographic projection is the standard approach.
Should include:
- A plan view of the generator room or area, with the DG set, the device, the exhaust route, walls, columns and doors
- At least one elevation showing heights: device, pipe, supports, stack and outlet
- A section through any congested area, such as a wall penetration or a place where the pipe passes other services
- For rooftop or tall installations, an elevation of the whole stack
- A key plan showing where the area sits on the site
- An isometric sketch where the route turns in several planes
Block 3: The existing installation, shown accurately
A retrofit lives inside an existing room. The GA must show that room as it really is, not as the original building drawing says it was.
Should include:
- The DG set outline, with the exhaust outlet position and height measured on site
- Existing silencer, pipework and supports, marked as retained, modified or removed
- Walls, columns, beams, doors, louvres and their sizes
- Existing cable trays, pipes, ducts and other services near the route
- Fuel tanks, day tanks and fuel lines
- Floor drains, trenches and pits
- A note of how the existing conditions were surveyed, and when
Many retrofit problems come from GAs drawn off old building plans. Our article on whether an RECD can be installed without cutting the existing exhaust pipe discusses working with existing components.
Block 4: The device envelope and orientation
Should include:
- Overall dimensions of the device, including insulation
- Orientation: horizontal or vertical, and flow direction marked with an arrow
- Positions of inlet and outlet flanges
- Positions of access doors, clamps and filter modules
- Positions of sensor bosses, pressure tappings and drains
- Nameplate location, so it remains visible after installation
Our guide on horizontal vs vertical RECD mounting explains how orientation affects layout.
Block 5: Connection schedule
A small table on the drawing listing every connection prevents a large number of site queries.
| Tag | Connection | Size and type | Rating or standard | Mates with |
|---|---|---|---|---|
| N1 | Device inlet | Flange, nominal size stated | Drilling standard stated | Upstream spool or bellows |
| N2 | Device outlet | Flange, nominal size stated | Drilling standard stated | Downstream pipe |
| N3 | Inlet pressure tapping | Threaded boss | Thread type stated | Impulse tube to transmitter |
| N4 | Inlet temperature sensor | Threaded boss | Thread type stated | Thermocouple |
| N5 | Outlet temperature sensor | Threaded boss | Thread type stated | Thermocouple |
| N6 | Drain | Threaded boss with valve | Thread type stated | Drain line |
| N7, N8 | Sampling ports, where on the device or stack | Nominal size stated | Cap or flange type | Laboratory probe |
The schedule should match the device data sheet exactly. Flange drilling mismatches discovered on site are among the most avoidable delays.
Block 6: Weights, centre of gravity and lifting
Should include:
- Dry weight of the device
- Operating weight, including insulation and a stated allowance for soot and ash load
- Weight of the heaviest removable part, usually a filter module
- Centre of mass position for the device, marked on the views
- Lifting lug positions and any lifting instructions
- The lifting route into the room or onto the roof, on a separate sketch if needed
The structural engineer needs these numbers. The installation crew needs the lifting points and route. Our rooftop RECD installation guide and the basement DG room planning guide both show how lifting routes shape layouts.
Block 7: Supports, anchors and loads
Should include:
- Support positions and types: fixed saddle, sliding saddle, guide, hanger
- A reference to the support frame drawing
- Reactions at each support point, or at least the loads passed to the floor, wall or roof
- Anchor types and positions
- Positions of anchors and guides on the pipe run
- A note identifying which support is fixed and which allows sliding
Fixed and sliding supports must be shown clearly. A GA that shows two identical saddles with no note leaves the fabricator to guess, and the guess is usually “bolt both tight”.
Block 8: Clearances and maintenance envelopes
This block separates good GAs from adequate ones. It shows the empty space the installation needs, not only the steel.
Should include, as dashed outlines:
- Filter withdrawal envelope: the space needed to remove the filter module, along its removal path, including any lifting gear
- Access zones in front of access doors, clamps and the controller
- Technician working space around flanges and sensors
- Clearance to hot surfaces from combustible materials and cable trays
- Door swings and escape routes that must remain clear
- Probe clearance in line with any sampling ports
If the withdrawal envelope crosses a wall, a pipe or another machine, the drawing reveals the problem before installation. Our RECD maintenance guide lists the tasks that need these spaces.
Block 9: Exhaust route and performance notes
Should include:
- The full route from engine outlet to stack outlet, with pipe sizes
- Positions of bellows, expansion joints, bends, reducers, the silencer and rain cap
- Slopes on horizontal sections, and drain points at low points
- Wall, slab and roof penetrations, with sleeve details referenced
- Insulation scope, shown by hatching or notes
- A note of the calculated total backpressure at rated load, with soot load allowance, and the engine maker’s limit
The backpressure note is short and important. Our explainer on how exhaust backpressure affects a DG set explains why every reviewer should look for it.
Block 10: Outlet, sampling and surroundings
Should include:
- Outlet height above ground and above the adjacent building, with the required height noted
- Outlet direction and rain protection type
- Positions of fresh-air intakes, openable windows and AHUs near the outlet, with distances
- Sampling port positions, with their distance from the last disturbance in pipe diameters
- Access to the sampling ports: ladder, platform or roof route
- Exclusion zones needed during testing
Stack height rules for DG sets are linked to building height and set rating; the GA should show how the outlet satisfies them. For why height supports dispersion without replacing treatment, see whether increasing chimney height is an alternative to an RECD.
Block 11: Electrical and instrumentation interfaces
Should include:
- Controller position and mounting
- Junction box positions for sensor cables
- Pressure transmitter position and impulse tube route
- Cable routes, at least in outline, with heat zones noted where relevant
- Power supply source, by reference to the single-line diagram
- Local isolator position
- Earth bonding points on the device and frame
Block 12: Notes, references and bill of materials
Should include:
- General notes: units, design codes followed, materials, coatings, gasket and bolt specifications
- References to all related drawings by number and revision
- A short bill of materials for the main items: device, bellows, pipe spools, supports, insulation, controller
- Hold points: items still to be confirmed, clearly marked, with who is responsible
- Hazard notes: hot surfaces, work at height, lifting
Hold points are healthy. A drawing that admits “HOLD: wall capacity to be confirmed by structural consultant” is more useful than one that pretends everything is settled.
The Reviewer’s Red-Pen Checklist
When a GA arrives for comment, work through it with a pen. Each line is a yes or no question.
| No. | Check | Block |
|---|---|---|
| 1 | DG make, model, serial number and rating match the nameplate | 1 |
| 2 | Revision, status and date are clear | 1 |
| 3 | Plan and elevation views show all heights and positions | 2 |
| 4 | Existing conditions were surveyed on site, with a date | 3 |
| 5 | Retained, modified and removed items are marked | 3 |
| 6 | Device dimensions include insulation | 4 |
| 7 | Flow direction is marked | 4 |
| 8 | Connection schedule matches the device data sheet | 5 |
| 9 | Operating weight includes soot and ash allowance | 6 |
| 10 | Centre of gravity and lifting points are shown | 6 |
| 11 | Lifting route into position is shown or referenced | 6 |
| 12 | Fixed and sliding supports are identified | 7 |
| 13 | Support loads are given for the structural check | 7 |
| 14 | Filter withdrawal envelope is shown and clear | 8 |
| 15 | Access zones and door swings are clear | 8 |
| 16 | Clearances to combustibles and cable trays are shown | 8 |
| 17 | Full exhaust route with bellows, slopes and drains | 9 |
| 18 | Penetration details are referenced | 9 |
| 19 | Insulation scope is shown | 9 |
| 20 | Total backpressure and engine limit are noted | 9 |
| 21 | Outlet height and direction are stated | 10 |
| 22 | Nearby intakes and windows are shown with distances | 10 |
| 23 | Sampling port positions and access are shown | 10 |
| 24 | Controller, junction boxes and transmitter positions are shown | 11 |
| 25 | Isolator and earth bonding points are shown | 11 |
| 26 | Related drawings are referenced by number and revision | 12 |
| 27 | Hold points are listed with owners | 12 |
Any “no” becomes a comment for the next revision. The list doubles as a fair way to compare drawings from different vendors when choosing CPCB approved RECD vendors.
Common Gaps Found in RECD GA Drawings
The floating device
The device is drawn neatly in the middle of a blank space, with no walls, no other services and no existing pipe. Nobody can check clearances.
Dimensions only to the device centre line
The drawing gives the centre line but not the insulated outside diameter. Clearances look generous on paper and disappear on site.
No withdrawal envelope
The device fits, but the filter cannot come out without removing a wall panel or a pipe.
Identical saddles
No indication of which support is fixed and which slides. Both get bolted tight.
Missing weights
The structural engineer cannot check the floor or wall, so either the check is skipped or the job stops while the vendor finds the numbers.
Silent on backpressure
No total backpressure figure. The reviewer cannot tell whether the route works for the engine.
Outlet shown, surroundings not
The stack appears with its height, but nearby intakes, windows and neighbouring buildings are absent.
No electrical interfaces
The controller appears as a box on a wall with no supply, cable route or isolator. The electrician improvises.
Many of these appear in our list of common RECD installation mistakes, because a gap on paper becomes a mistake on site.
From Rev A to Rev C: How Review Improves a Drawing
This is an illustrative case for a 700 kVA set serving a commercial complex in Ahmedabad.
Rev A: for comment
The vendor’s first issue showed the DG room in plan with the set, the device on a floor frame and the exhaust running to an external wall and up to the roof. It gave the device’s overall length and height, flange sizes, and a single elevation. The title block read “for comment”.
The client’s engineer, the structural consultant and the HVAC consultant reviewed it against the checklist and returned 14 comments. The main ones:
| Comment | Checklist item |
|---|---|
| DG serial number missing; rating shown as 750 kVA, nameplate says 700 kVA | 1 |
| Room survey date not given; a cable tray along the north wall is not shown | 4 |
| Device dimensions exclude insulation | 6 |
| No operating weight or centre of gravity | 9, 10 |
| Both saddles shown identically | 12 |
| Filter withdrawal direction not shown; north wall tray appears to block it | 14 |
| No backpressure figure | 20 |
| Roof AHU intakes not shown; outlet appears close to one | 22 |
| Sampling ports not shown | 23 |
| Controller position not shown | 24 |
Rev B: for approval
The vendor resurveyed the room and returned a revised drawing.
- Correct rating and serial number in the title block
- The cable tray now shown, with the device moved 450 mm south so the withdrawal envelope clears it
- Insulated dimensions, operating weight with soot allowance, and centre of gravity
- Fixed saddle at the inlet end, sliding saddle at the outlet end, clearly labelled
- Calculated backpressure, with the engine maker’s limit for comparison
- Roof plan added, showing two AHU intakes; outlet extended and moved to the opposite roof corner
- Sampling ports shown at a height reachable from the roof, with the straight run in diameters
- Controller and junction box positions shown
Three comments remained: support loads for the roof bracket, the isolator position and the earth bonding point.
Rev C: approved for construction
The final issue added support reactions for the roof bracket, the isolator position beside the controller and the bonding points on the frame. The revision table listed every change since Rev A. All three reviewers signed it.
Installation followed the drawing with no layout changes on site. Commercial complexes often have several tenants and building services teams; our guide on coordinating DG retrofits in shopping malls covers multi-party review. The 700 kVA DG set RECD page shows this rating.
Who Should Review the GA?
| Reviewer | What they check |
|---|---|
| Site or facility engineer | Existing conditions, access, operation, maintenance |
| Structural consultant | Weights, support loads, floor, wall or roof capacity |
| HVAC consultant | Outlet position relative to intakes, ventilation of the room |
| Electrical contractor | Controller supply, cable routes, isolation, earthing |
| Safety officer | Hot surfaces, work at height, lifting, escape routes |
| Generator service provider | Engine outlet loads, backpressure, interlocks with the DG controller |
| Environmental or compliance lead | Sampling ports, stack height, records |
Not every project needs every reviewer, but each concern needs someone. Our article on whether installing an RECD affects the OEM warranty explains why the generator service provider’s view matters.
After Installation: The As-Built GA
The approved GA shows what was planned. Sites change things during installation: a support moves 200 mm, a drain is added, a cable route changes. At handover, the vendor should issue an as-built revision showing what was actually installed.
The as-built GA becomes the reference for maintenance, inspection, future modifications and any later transfer of the device. Our article on whether an RECD can be transferred to another diesel generator shows why accurate records help if the device ever moves. Keep the as-built drawing with the device certificate and commissioning records; the RECD installation process lists the handover documents.
Compliance Note
CPCB’s System and Procedure for Emission Compliance Testing of RECDs sets out how devices are tested and approved. The GA is not an approval document, but it records which approved device is fitted to which generator, where the sampling ports are and how the installation was arranged. Inspectors and auditors often ask for installation drawings. Our article on what happens during a pollution control board inspection explains what they tend to look at, and the environmental compliance checklist for generator owners shows where the drawing fits in your records.
Frequently Asked Questions
What is a GA drawing for an RECD?
A general arrangement drawing shows how the device, exhaust route, supports and interfaces fit together in the real installation, with enough information to approve the layout and coordinate the trades.
Who prepares the RECD GA drawing?
Usually the RECD vendor or installer, based on a site survey, with input from the site’s engineers and consultants.
Should the GA show the filter removal space?
Yes. A dashed withdrawal envelope along the removal path is one of the most useful features of a GA, because it shows whether the filter can be serviced.
Why does the GA need weights and centre of gravity?
The structural engineer needs them to check floors, walls, roofs and frames, and the installation crew needs them to lift safely.
How many revisions are normal?
Two or three is common: a first issue for comment, a revised issue for approval and a final issue approved for construction, followed by an as-built revision.
What is an as-built drawing?
A final revision issued after installation showing what was actually installed, including any changes made on site.
One Sheet, Many Signatures
A complete RECD GA drawing is a coordination tool. It shows the real room, the device with its true size and weight, how it is supported, how it connects, where it needs empty space, where the exhaust goes and what it passes on the way, and where the electrical and sampling interfaces sit. Built around twelve blocks and reviewed with a short checklist, it lets every trade and reviewer find their answers in one place, and it turns installation day into the execution of decisions already made.
Aceget issues a full GA drawing for every RECD project, revised through review and closed out with an as-built issue at handover. To have a drawing prepared or an existing one reviewed, talk to Aceget, or browse the retrofit emission control device range.